Favorite Gym Leaders From Each Generation

Kanto: Brock, Misty, Erika, Koga
Johto: Whitney, Jasmine, Clair
Houen: Brawly, Flannery, Winona, Juan/Ardan
Shinou: Gardinia, Fantina, Candice
Unova: Burgh, Elesa, Clay, Skyla, Marlon
Kalos: Grant, Korrina, Clemont, Valerie

Most of the ones I like have a great personality--either visible in the games or developed in the show, or they were fun to battle.

 

Kanto - Giovanni, Lt. Surge, Blaine
Johto - Chuck
Hoenn - Roxanne, Wattson, Wallace
Sinnoh - Crasher Wake
Unova - Lenora, Clay
Kalos - Wulfric

 

Kanto: Sabrina and Erika

Sabrina is a boss and Erika gives flower loonies like myself a good name.

Johto: Jasmine and Claire

Jasmine is so benevolent taking care of that Ampharos. Being the first steel type gym leader also makes her fabulous. Claire is a dragon master with a gym full of lava.

Hoenn: Winona and Tate/Liza

Winona was so graceful and her Altaria was amazing! I was always terrified of its Earthquake. Tate and Liza are the cutest gym leaders and I love how they complete each other's sentences!

Sinnoh: Maylene and Fantina

Maylene may be small, but she can kick butt which is amazing. Fantina speaks multiple languages, competes in elite contests, and has a gym full of math problems. She is so well rounded its scary... like her ghost Pokémon.

Unova: Elesa and Iris

Elesa is hands down, the most fashionable gym leader. Both of her gyms were absolutely steller. I mean who wouldn't want to ride on neon lighted roller coasters or walk down a lighted runway with a huge crowd cheering? Iris was adorable and pretty amazing too. How many little girls in the Pokémon world do you know are dragon masters?

Kalos: Valerie and Olympia

Valerie brings lolita fashion into the Pokémon universe so she gets cool points for that. Also being the first fairy gym leader makes her even more so amazing. Olympia is so mysterious and beautiful. Her gym was so pretty and I loved the space theme she had going on.

 

Kanto: Sabrina. She seems to have a very calm, collected personality. Not arrogant or combative or anything, just confident in her abilities and willing to let you make a foll of yourself in front of her.

Johto: Jasmine. One of my favorites, I like how she was given a personality completely different from what I expected, like a hardcore machismo-fueled musclehead. No, instead she's just so perfectly happy, caring, and peaceful that her emotional stability corresponds to her Pokémon's defenses.

Hoenn: Ehh, I don't know. How about Phoebe from the E4 there? Kind of like Jasmine, I liked how she contrasted to my expectations. Rather than a spooky goth girl, she's a light-hearted spiritual type, and she does it quite well!

Sinnoh: I don't know if he's my favorite, but I think Volkner's approach was unique. So bored of his job constantly winning, he's not a hothead wanting to beat down his next opponent; nor is he overly bombastic with encouragement. He's kind of like "Yeah, whatever, I'll battle you. Just make it quick." A maybe refreshing contrast to the usual energetic leaders.

I haven't yet finished a Gen 5 or 6 game, but based on skimming Bulbapedia, I kind of like Drayden in Unova and Wulfric in Kalos. Drayden mostly for a pretty cool character design, and Wulfric for his honesty. He acknowledges that his mono-type team can mean a great challenge or a totally easy battle, something that all the other gym leaders seem to forget.

 

Kanto: Giovanni, because Ground is an awesome type and it's awesome that he duals as a Gym Leader and the Big Boss of Team Rocket.

Johto: Not a ton of memorable Leaders, but Claire is cool because dragons are cool.

Hoenn: Wallace. Wallace is fabulous.

Sinnoh: Fantina is fabulous too, and her Gym in Platinum was really really cool too.

Unova: Brycen is a freaking ice ninja, and a moviestar to boot.

Kalos: Another region with unfortunately forgotten Leaders, but Korrina sticks out to me most because Mega Lucario and plot.

 

Kanto: Misty she might be my favorite gym leader period and I love water types.
Johto: Morty He is a real challange considering his Pokémon aren't particularly high level also even though Clair is cooler, and dragons, she is also spoiled brat and refuses to give you a badge.
Hoenn: I really like the whole league they all can be challanging, fun, and memorable. But I think Norman is my favorite. He is so different as a character because you play as his child and so battling him is an intense experience and especially rewarding. When you win you feel like you have defeated a mountain and the mountain is both shock, dissapointed in itself and proud. Also unlike Whitney who was the first normal type gym leader, who usally only beats you by spamming rollout, Norman is pretty tough and his gym does a great job of explaining the advantages of using X items.
Sinnoh: Roark is possibly the single hardest first gym in any of the games. It took me forever to beat him I even started out with Turtwig and it was just impossible to take down that Cranidos. I think it was seven+ tries I've never take that many tries at a gym leader since I was playing the blue for the first time. I don't really recall my first playthough of diamond so this is based on my replay that I started this year.
Unova: Elesa Though this might change after I play Black 2 or White 2 I haven't had the opportunity yet.
Kalos: I really like all the leaders in this one but that might just be because of the amazingly unique 3D gyms. If I had to choose it would probably be Korrina. Since she does double duty in the games as not just a gym leader but also as the person who gives you your skates and Give you one of her Lucarios with a mega stone.

Honeslty as much as I love the classic gyms Game Freak seems to make better Gyms and Leagues with every generation and work gym leaders into the story lines so they really fill out their roles. I cannot wait for the next set of leaders, whether we get some fresh faces in the next part of this gen or new ones in the next is reall the question.

 

Kanto-Brock
Johto-Claire
Hoenn-Roxanne
Sinnoh-Fantina
Unova-Elesa
Kalos-Korrina

 

Kanto - Brock, mostly because I like him in the anime and mangas though. XD
Johto - Whitney, she looks nice
Hoenn - Tate and Liza, they were cute and fun to battle
Sinnoh - Candice
Unova - Cilan
Unova 2 - Cheren
Kalos - Clemont