wow i'm surprised at how many people had gen 5 as their least favorite;;
Main reasons why 5th Gen gets hated a lot is due to "terrible" Pokemon designs and claims that the story in Black/White is too linear.
As for my thoughts...
1st: Generation V (Unova)
Now yeah, I know this generation gets hated a lot for what I mentioned above, but this is actually my fave generation to be honest, well it did introduce my fave Pokemon of all time (Oshawott you are da bomb) plus I love how modern-looking Unova is, while still mixing in some rural areas. If people think the story is too linear, you might enjoy B2/W2 more since story is less linear than B/W. I also loved the new areas they had in B2/W2 as well, not to mention those games having one of the most addictive postgames ever. And I don't think the starters look horrible at all.
2nd: Generation VI (Kalos)
I know I haven't played X and Y yet, but I've already seen how beautiful Kalos looks thanks to screenies on Tumblr and YouTube videos. The new Pokemon, while introduced in a small number, won me over a lot with great designs and everything. Plus, I fell in love with the Fairy-type quite quickly unlike most people. And best female game protagonist ever since Dawn (yeah Serena you are a badass with fashion sense) means I am definitely excited for when I eventually do play X and Y.
3rd: Generation IV (Sinnoh)
This was a great balanced generation imo, while Diamond and Pearl lacked heavily, Platinum fixed all of that. And of course, this generation introduced my first real love of a human character in the games (Dawn) as well as some interesting new Pokemon. I know many bash on this generation for having too many Legendaries, but I love how well the starters were designed, plus they had some cool typings as well. I loved how beautiful this region was and I eventually want to replay Platinum again sometime.
4th: Generation III (Hoenn)
My first generation as far as playing the games goes. The starters' designs I had mixed reactions on at first, but despite my noob state when I first played Ruby, it was my first game where I caught a shiny and beat the main story. I love the nice tropical feel Hoenn has, and all that trumpet-influenced music makes it a memorable generation for many. Still, it seems to fall for me when new generations get released.
5th: Generation II (Johto)
I wasn't a fan of most Pokemon in this region, plus there was quite a small number of new Pokemon as well. The Gym Leaders were also among the toughest here, and I didn't even play the 2nd Gen itself but I did play HG/SS which sorta comes close. At least the Japanese-inspired design of Ecruteak City saved me there.
6th: Generation I (Kanto)
Ah yes, the one that started it all apparently ended up bottom of my list for various reasons. I wasn't a fan of the Kanto starters, but their Megas in 6th Gen are making me show more faith in them lately. Most Kanto Pokemon didn't have great designs, and the eyes weren't as cute as future Pokemon. Plus, it's overrated as heck and I never even got the chance to play a proper Kanto game (nope HG/SS doesn't count for me here). Hence why Kanto was my least fave here.
So yeah, I'm a reverse Genwunner or something? I'm someone who actually loves the newer generations more for a weird reason. Very unusual but true...