Hardest Gym Leader?

I voted Kanto because of Blue in SS. Took me 2 times to beat it. Which I usually get all of them in 1 shot.

Johto.. You know, I gotta say, I ace'd most of them. Whitney's miltank was no problem >:D
Hoenn: I dont really remember anything from it, Except the one in that city before that small city was hard. Cant remember names or types because I was like 4.
Sinnoh: Maylene for her lucario. I think it usually takes me about 4 times to get it? And that ice one. Can't remember her name, Butit kept coming back on Torterra x Froslass... (Spelling?). It took me like a whole month to beat it. My torterra was at lv 58 by the end of that, Which is E4 worthy XD
Unova: Elesa takes the cake. Sooooooo.... Harddddd..... Stupid volt tackle took me down a lot ¬.¬ It was so fast!

Well... Hmm... Lets see now...

Kanto: I usually never had any trouble with most of the Gyms, but I would definitally say Brock and his freaking Onix. At least Charmander users can damage it, but try using a Pikachu! Sabrina also gave me a crap load of trouble in Firered because of her Alakazam.

Johto: Probably my ultimate downfall was picking Chickorita as my starter, but it was cute. I lost against almost every Gym, probably because of this. Although, I would have to say Bugsy and his Scyther because of that freaking overpowered U-turn, or Clair, with that Kingdra. You know how it goes with Kingdra.

Hoenn: Training only one Pokemon wasn't the best idea against Tate & Liza. Their Psychic-Type Pokemon, espically Lunatone and Solrock, gave me a heck of a battle against my overleveled Blaziken. Even though I was at a type disavantage though, level prevaled, and I won!

Sinnoh: Candice and her Abomasnow and Frosslass. Abomasnow gave me a problem against my Empoleon my first play through of Platnium, and Frosslass gave me a problem too in my second (or third) walkthough of Platnium.

Unova: Like Johto, picking the Grass-Type starter comes back to haunt me. *Sigh* Anyway, Iris gave me a problem in White, pretty much because I didn't want to back track and I was relying on one Pokemon to beat her, so you can see where that goes, huh? But in Black, I have no idea. I guess my Axew and Deino proved to strong for the region, eh?

Yeah, I guess thats how I feel about it. I think BW2 Will be tougher though.

I voted Johto. That damn Miltank is haunting me to this day.

I can never really remember having any serious problems with Kanto, Sinnoh or Unova gyms. Probably the biggest step up in Kanto is fighting Sabrina, chiefly because Psychic Pokemon had so few weaknesses. Seriously, it was just bug and that was it! Sinnoh... I remember Fantina being a bit hard but a big of grinding sorted her out. Unova... there wasn't really anyone who I felt hopelessly overwhelmed by. Elesa and Lenora are probably the most awkward, but it's easy to outlevel them thanks to Audino.

Whenever I think of hard gyms, I think of Johto and Whitney. I think I speak for many people when I say I had my Pokemon handed back to me in pancake-shape thanks to her bloody Miltank. Norman was really hard too in Hoenn. I struggled with him big time. More often than not Normal Pokemon = Grinding for a long time.

Hoenn was the hardest overall, though.

I guess I have to say Kanto because of Sabrina in Pokémon Stadium. It's obvious though, Psychic was way overpowered and broken in Generation 1.

They've all been fairly challenging, considering how much I train (not a lot at all), and Whitney's Miltank has always been a pain, but luckily I could get a couple Thunder Waves on it with my Flaaffy (damn berry), Morty was never any trouble with my Feraligatr's Crunch, and Norman always gave me trouble. Amazing how Normal-types are always the hardest, and we've been underestimating these Rattata and Bidoof for years...

Opelucid Gym. I had so much trouble trying to navigate the freaking gym!

I'll have to go with Johto. Whitney's Miltank was problematic for me in G/S/C and Clair's Kingdra was really tough to beat as well. Maybe it helps that Silver was my first Pokemon game and those Gyms were a bit more challenging partly because of being inexperienced, but Johto is the only case where I can remember having a tough time in two Gyms. In Kanto, I only had problems against Brock since I would start off with Charmander, or Pikachu in Yellow's case, and there wouldn't be anything else to help me out. None of the Gyms in Hoenn or Unova come to mind as problematic come to mind and I remember only having problems with Candice in Platinum.

Apart from Whitney, the only one that really stands out in my mind is Juan and his horrible, horrible Kingdra. That double team spam just made the whole thing impossible.

I picked Hoenn.

Kanto: I had lots of problems with Brock and Misty, mostly due to the fact that I would not pick a starter other than Charmander. :D

Johto: I couldn't defeat Jasmine. That stupid Steelix was overpowered. Claire and Whitney were hard too.

Hoenn: Tate and Liza were really difficult. I had to train a looong time. Norman kept killing me with that Slakoth, too.

Never played Sinnoh or Unova.

heonn was so hard for me it broke my streak of beating every game in 1 week after release
unova was extremely easy except for elesa.

Kanto: Brock, especially if you chose Charmander
Johto: Clair, her Kingdra hits too hard. (I've never found Whitney that hard)
Hoenn: Tate and Liza, between their annoying Earthquake and Psychic combo, and their Calm Mind spam.
Sinnoh: Maylene, her Lucario is fast hits too hard.
Unova: Elesa, because of one thing: "Emolga" and two words: "Volt Switch"
Overall: A tie Between Maylene and Elesa, a double battle between them would be my worst nightmare.

Gen1 Sabrina, hand's down, then again thats what I get for trying to challenge her before even facing Erika e_e
Gen2I don't get Whitney, OP a pokemon and Miltank goes down, no, no, it was Jasmine and her freaking Steelix D;
Gen3 Lisa and Tate; I had to train a sharpedo to finally take them down
Gen4 Fantina and her stupid Mismagius e___e
Gen5I uh.... honestly don't remember anyone in Unova giving me trouble.....

Johto. Do you know why? I'll tell you why.
That pink piece of rotten beef. The bane of my existence.
Whitney's Miltank.

Uuuuuggggh...I got lucky my first shot, my Quilava survived with 2 HP and outsped the thing, but my team was ravaged. My eternal hatred for Whitney continues to burn.

I voted Unova, mostly because of the Striaton and Nacrene Gyms. I've played through Black/White many times, and those two Gyms have always given me a hard time. I dislike that we have to rely on the elemental monkeys for the Striaton City Gym battle, and Lenora's Watchog has always been a beast in my opinion.