I'm still relatively new to the PokéSpec manga (I know, I know, but when I was crazy over Pokémon as a kid 'twas those dark days before eBay was invented, and as I come from a tiny town in England, the chances of my discovering it then were practically zero) so I haven't even scratched the surface of all of the characters yet D: But, so far:
Emerald. I originally bought the Emerald chapter because Battle Frontier hooooo~!, but the more I read it, the more I love Emerald ^.^ He's so cute and enthusiastic, and I love the Inspector Gadget look he's got goin' on. :]
Blue♂. His eyes are lovely. I love his kick-ass personality. :3
Professor Oak. He's been one of my favourite characters in the games/anime since I first started playing/watching them, and I love his portrayal in PokéSpec, however short it tends to be.
I'm going to start on the G/S/C arc next year, as Silver interests me greatly and I want to see why people have such divided opinions over Gold ^.^