The best of the best!

[Lynnx]

My favorites are Steven and Cynthia, who I like because they actually interact with you outside of the League as opposed to just sitting in a room. (Well, I guess Blue/Gary does that too, but he's your rival. :P)

 

[True Reign]

Gary has been the hardest in my opinion. I have not played D/P/P yet, so yeah...

I can already tell that that Alakazam is going to be in the pain in the butt after my training for the second time.

 

[ErickaVolt]

The best is Cynthia for me, her team can own you. She's pretty strong.

 

[Spectacular Hero]

I like Steven, he's a great classic and really strong

 

[Legobricks]

Lance because he actually does things with the player character prior to reaching the Elite Four.

 

[Espeon Master]

Gary/Blue/Rival.

He has the strongest and most well balanced team in my opinion. Not to mention I love the pokemon he has.

 

[Caelus]

Definitely Lance. When I first battled him I nearly lost to his third Dragonite--and was thinking of giving up--but my Poliwhirl somehow managed to faint it, and it ended up becoming my favorite battle. Sure, the other three have a nice team, but Lance is just the one that I find to be the most "impressive".

 

[XaRhS]

I'll go with Wallace. However, i hate water-types, it's just that all of the others didn't make any impression on me. And we have to admit, Wallace was a tough Gym Leader.

 

[Azonic]

I'm gonna be a biased competitive battler here and say that none of them were actually decent. The first one (rival) was probably the strongest though because his Pokemon actually leveled up after the first battle.@_@