5th Gen How Would You Rank The Difficulty of Unova Gym Leaders?

You can add both BW and B2W2 if you would like, or if you would just one game, that is fine.

BW

1. Drayden/Iris - They just... Never... DIE. Maybe it makes me a bad player, but I had to stall with Toxic for this battle.
2. Lenora - Retaliate has a good chance to OHKO any Pokemon at this point in the game that would not be Roggenrola. But why would you catch that?
3. Elesa - Oh, you brought Servine to resist the electric? She does not have a Pokemon with Flying type STAB... But two. Oooooooo...
4. Burgh - Leavanny can deal a surprising lot of damage with Razor Leaf. The rest of the battle however, is managable.
5. Skyla - She is similarly to Burgh, in that Swanna can deal great damame with Bubble Bean the other two Pokemon aren't too much trouble. Medium range difficulty.
6. Brycen - Once again, the most dangerous Pokemon, which is Beartic here, is the only major threat. However, Beartic has bad speed, which placed Brycen lower than the other two.
7. Clay - Even Excadrill wasn't a threat... Just bring a Water or Grass type.
8. Chili/Cilan/Cress - They are compared unfavorably to the more successful monkey that's handed to you before the battle.

B2W2

1. Drayden - The same reason as before. Luckily, I did require to use Toxic here.
2. Cheren - I have no clue what happened... He just swept my team with Work Up...
3. Skyla - Now that she brought in Skarmory, the battle can actually be a problem without an Electric Pokemon.
4. Elesa - She got easier, but Static can still give you problems. Also, apparently Electric Pokemon can get paralyzed, at least in fifth generation.
5. Marlon - Its pretty late in the game for a Pokemon with just Water Pokemon, though they are all quite bulky and can take hits.
6. Roxie - Magnemite.
7. Burgh - Why would you replace the Whirlipede with Swadloon? Now two of your Pokemon are 4x weak to Fire attacks.
8. Clay - And now, all of your Pokemon are weak to Samurott. Great work Indiana.

Have fun.

I don't think that was that hard, at least I don't remember of me having a hard time. I also don't remember my team, except for Tepig 😁

I'm actually not sure of rankings for each of them, but I definitely suffered the most battling Lenora so I'd rank her 1. For 2, probably the Striaton trio because of the type matchups being a bit of a pain at the start when my starter was not yet evolved. Thank goodness for the monkey given to you tbh.

So..

1) Lenora
2) Striaton trio
3) Burgh, which I struggled with when I didn't have a fire type
4) Everyone else?

I don't remember having many difficulties with the rest. But Lenora aaaahhh.

BW1

1. Drayden / Iris - Haxorus is a prettty big threat considering it has Dragon Dance for sweeping potential, also the amount of Pokemon that can reliably deal with Dragon-types within this game are few in between
2. Elesa - Volt Switch spam is obnoxious and even though the game does provide Ground-types prior to the gym, it's kind of moot considering she has 2 Emolgas that don't care about them. Also Grass-types you would use as a resist also get bopped by her Emolgas too
3. Lenora - Retaliate hits very hard and as OP mentioned, not many good resists that can actually sponge a fully powered Retaliate. Ranked her below Elesa because Pinwheel Forest does provide a decently reliable way to deal with her team (Throh, Sawk and Timburr)
4. Clay - Excadrill is pretty scary with Hone Claws and there aren't that many Pokemon that can reliably deal with it but, his other 2 Pokemon are very easy to deal with.
5. Skyla - Swanna and Unfezant are probably the big ones to look out for but still are pretty easy to deal with (especially if you caught stuff at Chargestone Cave)
6. Burgh - Leavanny's Razor Leaf can hit hard but Struggle Bug is kind of moot considering his entire team is more physically offensive? Was pretty easy overall from my experience
7. Brycen - His team is slow but also not very threatening (aside from Beartic maybe), Ice-types are also very easy to deal and his Vanillish is easy setup fodder since it's pretty weak
8. Straiton Trio - You get handed a monkey to deal with their ace

BW2

1. Drayden - If anything, his team got stronger with the addition of Flygon replacing Fraxure. Haxorus is still a big threat with Dragon Dance and despite the expanded dex, there aren't that many Pokemon that can reliably deal with Dragon-types
2. Cheren - Lillipup can sweep unprepared teams with ease with enough Work Up boosts, also the one Pokemon that can deal with Cheren (Riolu) is rare af sooo...
3. Elesa - Flaaffy is definitely a step down but she's still a pretty big threat with her Volt Switch spam along with Emolga + Zebstrika like in BW1. Emolga losing Aerial Ace kind of sucks too (for her)
4. Marlon - Carracosta can sweep teams considering it has both Sturdy and Shell Smash. His team can also be annoying since his other Pokemon are pretty bulky, with Jellicent having Recover to prolong itself
5. Clay - Excadrill lost Hone Claws but it still pretty scary to deal with. Losing Palpitoad is unfortunate since you can bulldoze him with Water-types (which are more accessible in this game than BW1)
6. Skyla - Imo I thought Unfezant was a big threat than Skarmory but, Swanna can still be problematic. Overall still not that hard of a fight I found
7. Roxie - Would be annoying if she had ways to utilize Venoshock to its full potential, also Magnemite kind of sits on her
8. Burgh - Swadlon replacing Whirlipede made his team easier if anything considering Whirlipede could annoy you with status conditions in BW1, Leavanny's Razor Leaf can hit hard but there's a lot of resources that can deal with Burgh's team now

It's not hard if you stick with one team of at least 4 mons and have type advantage moves. But, of course, expect that some of them will be knocked out sometimes. If the gym leader have any buff move you have to be extra careful

Thought nimbasa gym was quite tough. Easiest being aspertia gym.