Toughest Gym Leader

[Mystical Jackal]

Whitney. When Miltank's Cute Charm is activated, defeating her gets harder!

[Usehydropump]

Whitney. WHITNEY, WHITNEY, WHITNEY, WHITNEY, WHITNEY

Her Miltank gave my nightmares (not literally, but you know what I mean). It took me to think harder than I ever thought when fighting a gym leader. In the end I came out victorious, of course.

[Sealotic]

I found the gym leaders easy, but I trained more before Clair's gym, so I would say that she was the hardest.

[xEryChan]

Whitney. That Miltank was a pain in the neck.

[Papousse]

Well, Whitney wasn't hard, since all my Pokémon were female at that time. Gym Leaders were all easy, except for Bugsy and Clair. Clair was a little more competent than the others. She shows off her skills more easily than the others (oh that annoying Kindra...) and that why she is qualify as my thoughest Gym Leader challenge in this game.
As for Bugsy, it's really personnal since I only got Bayleef and Togepi for this one and it was rough enough.

[Ke$ha]

I hate Whitneys gym because of her strong Miltank that always beat my Pokemon. I wish it didnt have Attract and Rollout but maybe the game programmers wanted to create a early challenge for the players or some thing so they gave it strong moves. I also had a hard time with Clair but mostly against Kingdra

[Auaria~]

I mainly struggled with Clair my first time around, but after my restarts, I've been having trouble with Whitney. Her Miltank always spams Milk Drink..

[The Musician]

I recently started a SS nuzlocke and had the EASIEST time with Whitney. All I used was a lvl 25 female Graveler and wiped the floor with her.

Clair is definitely the toughest for me since I normally don't end up with someone who can learn an Ice or Dragon-type move.

[Hankka]

Blue. That Machamp was a total douchebag.

[PikachuFan6]

I hated the Miltank and the final gym the dragon type.

[golduck#1]

If anyone says anyone but Whitney you are lying to yourself. Claire was easy for me mainly because I had a Jynx and a Magneton. Pokemon become so much easier to battle when they are paralyzed.

[Shayminlover123]

Clair.That Kindgra was something else and the only thing I had at the time was a High level Feraligatr.

[Silicone]

None of them were very hard, but lost two potions to Whitney :/

[TotodileAgent]

It's gotta be Whitney! She is always a real challenge for me! Seems like everytime I'm about to make her Miltank faint it heals itself then uses Rollout and Cute Charm to destroy me.

[Prophet800]

Blue. Hands down. Although none of them were very challenging... I call bugsy to pick on him when I need quick level ups

[Red Moon]

Clair, because of Kingdra.

[FlareLover17]

Whitney and Clair. Whitney's Milktank was.. a tank in battle basically. And Clair's Kingdra.. i have no words.

[Chriiis]

Even though Whitney's Miltank is pure evil, I'd have to say Bugsy was annoying the first time I faced him. I'm not too much of a grinder in the beginning of the game, so I was a little under-leveled. It didn't help that his Scyther kept landing critical hits as well with it's love of using U-turn.

[Grassmaster411]

Whitney. OMG, i seriously wanted to punch her in the face. Not only was her milktank almost impossible to beat, but he clefarily spams metrenome.

This story is 100% true. I had sent ouy my traded over grovyle (lv18) as a starter. He was facing her clefairy. I swear, the thing used metrenome, and it turned into Dreco FREAKING Meteor.

[Monster Guy]

Clair and Whitney.

Miltank and Kingdra + Dragonairs.