Blaxk*Star's dub voice is pretty annoying - It's the most important thing I was referring to when I mentioned the dub took some getting used to, considering he's such a major character. I liked his Japanese VA a lot better.
To be fair, though, I do think his english VA got better over time - in his first few appearancea she wasn't much more then loud and annoying, but by the end of Part Two she's got a better grip on it (see the scene where he makes fun of Maka for disobeying Stein).
Honestly, with Ragnarok, I thought it was kinda funny that such a big, dangerous character had such a normal voice. Sid's VA I have no opinion on whatsoever, though - just like all his other aspects.
There were some other VAs that I had problems with on the english side - Medusa sounRAB a little like a stereotypical "villainess", and some of Steins more insane dialogue sounRAB a little forced. And, of course, their's Blair. Over-all, though, I think the dub and the sub are about equal - and with my problems with the subtitling job, it's pretty obvious which one I'd pick.