Eh, I pretty much love all Flying type trainers, since they've chosen the best type possible, but I'm gonna go with Falkner here. In all honesty, he wasn't really that memorable, and his team was waaaay too easy to get through in G/S, granted you had the right Pokemon (ie, no underleveled Chikorita ); ), so that's not really the reason why I'd choose him. The reason lies more in the fact, that the second generation is basically where most of my time in the Pokemon universe has been spent, and thus I'm just more used to the gym leaders of the generation. I lost my Ruby before I even got to finish the second playthrough, so half of the gym leaders I coudln't even remember untill I got to play it again, Winona included, and I didn't get to play a fifth generation game before B2/W2, and I've only played through that once, so only thing that I really remember about Skyla is her gym and her darn Swanna. And I honestly didn't like her attitude in the anime <____>
So yeah, it's not because the other two aren't great characters, Falkner is just the gym leader I'm most familiar with.