I haven't watched a lot of BW in English, but from what I have heard, I don't really like Axew's English voice. And I can't believe so many people hate Tepig's English voice! I think it sounds ADORABLE. I love its little pig squeaks! I like his Japanese voice too. They both sound so cute. D:
I have more of a problem with the human characters when it comes to the dub voices, but the one I really can't stand is James. I just really dislike the voice actor that took over when TPCi took over after 4Kids. Maybe it's just because I really, really loved Eric Stuart as James, but I can barely stand listening to him in the dub now, he makes me cringe. I prefer his Japanese voice WAY more now that I've been watching BW in Japanese, which is good because I love James and it's hard to listen to him or take him seriously at all in English. >.< Jimmy Zoppi's Meowth is pretty terrible too, but not AS bad as James. I don't really like Iris' English voice either (she sounds a little too forced sometimes), but other than that, most of them are okay.
I used to hate practically every TPCi voice actor, but that was when I was still whiny over the fact that they got rid of all the 4Kids VAs. Aside from Zoppi, most of them are okay now.