I like Wallace. Just as a Gym leader. He seems to suit the title "Gym Leader" more than "Champion". Plus, he's one of my favourite Gym Leaders.
However Steven is badass, and I like him better(It's close though), I must say(Hmm, it seems like I'm the only one who hasn't really seen him "bland" as such). He has the whole "Champion" thing about him(Unlike Wallace, who really just seems more "Gym Leader ish" IMO)