Been a long time since I've posted new rankings and seeing as SuMo has released more, I can evaluate it a bit more. As always, this is my opinion and where a series is ranked doesn't mean its a bad series but only that something has to take the bottom rungs.
#1: Diamond&Pearl(Sinnoh Region, Seasons 10 to 13).
Ash, Brock and Dawn.... what a trio as they say. Although Brock was largely in the background at this point, he did have his moments and none more memorable when May returned for the Wallace Cup. His one liner in Full Course Tag Battle on May... priceless. Ash's team was pretty darn good. Although not fully evolved like his team in the next region on my list, he had more than a full team of 6. Staraptor, Torterra, Infernape, Gliscor, Buizel and Gible all had their own unique contribution to the series(none more than Gible in my eyes. Poor Piplup).
Out of all the female leads, Dawn might be the most polished and developed character of them all. Cocky and inexperienced to one of humility and elegance. Her team wasn't a slouch either, including an infamous Electric Squirrel if Pokemon World Championships are anything to go by. Her Contest Theme is by far my favorite and her chemistry with Ash was unparalleled. Tack on Paul as the best rival bar none and Cynthia as best Champion(and waifu) and you got a series that deserves the #1 spot.
#2: XY/XYZ(Kalos Region, Seasons 17 to 19).
Amourshipping for life!!! Now with that out of the way, back to objectivity. Ash's team in Kalos is one of my all time favorites and arguably his strongest due to the fact it was fully evolved with
two Dragon Types. My only knock, if there is one, is that neither Ash or his companions had a full team at any given time prior to the League. Serena, in particular, was an abject disappointment in that she took 46 Episodes to catch her first Pokemon and ended the series with just three overall. Unless that was deliberately done for a future return, I can't let that go. Her arc was also not as ideal as past Female performer leads as it was for the title of Kalos Queen, something that Males or Ash in this case, couldn't partake in. For a series with a romantic subplot... could you imagine Serena in a contest with Ash? I mean Ash participated in contests with May and Dawn. Why leave such an opportunity on the table? Despite that, Serena was still a memorable character with many, many infamous scenes, including this notable gem:
I'll add that all 8 Gym Leaders and their respective bouts with Ash are all memorable, although Ramos and Grant were at best average. The rest... oh boy were those good. Shoutout to Korrina for [user]LadyJirachu[/user]. Also Bonnie was a far, far better fourth wheel with her "You're a keeper!" gag that evoked memories of Brock. Excellent series that I'd recommend several times over.
#3: Advanced(Hoenn Region, Seasons 6 to 9).
Hoenn region is honestly not that bad. I mean sure Max is a useless fourth wheel but Ash's team was pretty decent, including Pokemon that most of us probably wouldn't use during a Ruby or Sapphire run. His powerhouse wasn't Pikachu but Sceptile and why wouldn't it with a Leaf Blade like that? Combined with Swellow, Torkoal, Corphish(why wouldn't you evolve?!! *cries*), and Glalie, Ash just had enough Pokemon to fill out his roster. His Hoenn League result left much to be desired but Battle Frontier more than made up for that.
May was the new breed of Female protagonists as she was the first playable character to join Ash on a journey. Although replacing the much beloved Misty, May was a pretty solid character who grew over the course of four seasons. While she did exhibit a lot of Ash's qualities, she was still her own confident self with a team that honestly I would use for a Hoenn run. Her return during Diamond and Pearl was also meaningful as she demonstrated that she had come a long way since departing from Ash. Plus May and Dawn together would have made for a pretty respectable side series if TPC had their act together. I'll conclude by saying that although the Gym Leaders left much to be desired(ThunderArmor anyone?), the Battle Frontier arc was exceptional. Brandon is probably the most notable with the Regi's but the rest of the Frontier Brains are no slouches either.
#4: Original Series(Kanto&Johto Regions, Seasons 1 to 5).
The series that started it all in Indigo League combined with the region that many regard as the best in Johto. Ash was a newb and hence we can forgive his immature and rather reckless behavior. We can even forgive the Anime's sins when it comes to Typing(Pikachu defeating a Geodude with "Thunderbolt"?!!!!!!) or the fact the Gym Leaders(in Kanto anyway) were an abject joke. Johto Leaders were better but Kanto... ugh. Honestly wish Ash would go back to Kanto and rechallenge the Kanto Gyms to redeem himself and for the Anime's sake. To this day he still hasn't earned that Boulderbadge in my eyes. He did beat Misty in SuMo43 so I suppose that counts for his Cascadebadge. Perhaps what Misty's sisters said in Episode 7 of Indigo League was very early foreshadowing. Still leaves Erika, Sabrina and whomever runs the Viridian Gym. Heck we might include Fuchsia Gym if Janine is running it now.
Ash's Kanto team is one I used in my first run through Pokemon Yellow and there's really no reason not to. All three Kanto starters are really good, although only Charmander evolved to ultimately become Ash's regional powerhouse. Butterfree is my favorite Bug Type and Pidgeotto(ultimately Pidgeot) is the first of Ash's regional Flying Types. If there is one knock on Ash is that Ash rarely rotated his Pokemon so Krabby, Muk and Tauros(which if you didn't watch the Japanese Dub you didn't know he had, much less 30 of them!!) didn't get any screen time until the Pokemon League where they inexplicably defeated opponents that were much stronger or had a type advantage like in Krabby's case. Then there's Primeape who lasted all but a few Episodes before never to be seen again...
In Johto, Ash swapped his Kanto Pokemon for those from Johto, including all three regional starters. Like with Kanto, only one of them evolved and only to its middle stage. You'd think they'd evolve it all the way but nope. At least Ash got Heracross and an OP one at that. Gary was Ash's rival through both regions and what I compliment Paul for doing during Sinnoh I knock Gary for during Johto and especially Kanto. The rival is meant to challenge the protagonist and Gary didn't even do that during Kanto, considering Ash to be a waste of his time. It wasn't until prior to Ash heading to Johto that Gary challenged him to a 1v1 wherein he wins. After that they don't even face each other until the Silver Conference. For a rival that's... kind of pathetic. I do love Gary's attitude with the poetic jabs("Gary was here, Ash is a loser") but he could have done far more to challenge Ash from a rival standpoint.
Other comments of note were the OST. Both Kanto and Johto... so good. Love this theme to death:
Also, Ash vs. Misty early on was really really good. The fact they fought so much was why Misty became a beloved character, even if she hardly did much besides a few Fishing contests and Whirl Cup when it came to her goal. Still hold Brock in high regard for having my favorite Pokemon of all in
Vulpix. Shame he had to give it back *cries*.
#5: Black&White(Unova Region, Seasons 14 to 16).
Years ago this region earned my Black Sheep title but alas, no more. Ash suffered one of the harshest resets to date in Unova and although Pikachu had a handicap removing its Electric attacks, it still shouldn't have lost to a starter Snivy. Although I do like Ash's companions, Iris' "You're such a kid" grew old pretty fast and became hypocritical at times thanks to Iris' own immaturity. Cilan's eccentric theatrics also grew old pretty fast but they were better than Brock's wooing of every girl/woman he comes across. At least Iris didn't put up with Ash's Bull$**$ and unlike previous regions, Ash went wild on catching Pokemon. Not including Pikachu or Charizard, Ash caught 9 Pokemon and most of them got much needed screen time. Even the Pokemon to Pokemon and Pokemon to Human interactions were a plus here but only three stood out: Ash's Oshawott and Snivy and Iris' Emolga. The rest had their moments but none more than those three. Just wish Iris got better treatment. I mean if Misty got a full team of Water Types, why couldn't Iris get more than just four Pokemon overall? Gible doesn't count being its post-series content.
Gym Leaders in Unova were average to below average honestly. Only Lenora, Elesa and Roxie showed any real competency while the rest were pushovers in my eyes. Even Trip was a Paul-wannabe and rivals for Iris and Cilan? Eh why were they needed? If Brock and Misty never needed them, then why and give Iris and Cilan rivals when you're, in effect, trying to recreate the atmosphere of Kanto with the two "Gym Leader" companion dynamic? Finally Ash's result in Unova League remains the biggest disgrace in the Franchise's history.
#6: Sun&Moon(Alola Region, Seasons 20-22(ongoing).
Sun and Moon is still ongoing but I think its safe to say that its unlikely to ever break out from its placement in the cellar. The change in Art Style, the increase in companions from 3 to 5, the lack of Gyms or traveling, few Pokemon catches, Z-Moves and "Ash-Pulls" that previous series weren't plagued by ultimately will leave here in last place. Let's start with the Art Style. I hate the Art Style. Animation wise, SuMo is arguably the best there is but Art Style along with the goofy faces and gags... is just too childish for my liking.
Increasing the cast from 4 to 6 meant that on any given Episode, at least half or so are pretty much shoved into the background and more often than not the focus is on Ash(which makes sense) and Lillie(arguably the main Female lead in the region). The other four, all Trial Captains in the games, are pretty much left to their own devices and only two of them(Kiawe and Lana) own Z-Rings and three of them have more than one Pokemon(Sophocles can thank Ash for Charjabug(now Vikavolt)). Mallow does indeed have Shaymin right now but its not "caught" so technically its not hers per se. Lillie is assumed to finally be getting her 2nd Pokemon next week, which would be 102 Episodes between getting starter and their 2nd Pokemon, a Franchise record.
SuMo did change the dynamic by removing Gyms for Grand Trials but the Anime opted to remove traveling altogether and thrust Ash into a Pokemon school, something that they've explicitly said on several occasions that Ash doesn't need, much less want to go through. AKA it doesn't make sense!! Why remove the traveling aspect? Could have had him go to Melemele first, then Akala and so on and so forth without all the backtracking or jumping around from island to island every Episode or so.
Finally there are the "Ash-Pulls" or victories that Ash never should have gotten that make ThunderArmor look like child's play. Defeating the UB with a Pikachium-Z, winning against Mimikyu with Electroweb and Hapu's "Soak" was the worst. Its not a bad series, just seriously flawed.