Ash bores me. Naetle bores me. So they're outta the picture.
I adore Pochama's entire personallity and odd mannerisms, as well as it's squabbling with other pokémon and it's trainer. However, I can't honestly say I like Hikari at all. She's not really done much to make me like her, and I feel that, for the moment at least, she's just there. So those two kinda missed the mark.
Shinji is a total badass who treats pretty much everyone like dirt, and is the first real rival in this show to have such an interesting personna. Hikozaru is awesome because it's a wacky chimp that gains sadistic enjoyment from pummling it's foes and because it has a flaming buttocks. It (currently) also has the most interesting movepool of the three starters
So Shinji and Hikozaru it is!