I'm still trying to figure out why Anakin and Vader have different accents. And to bring this round to the actual discussion, Vader's accent sounds Southern without the drawl...more clipped, which makes it intriguingly difficult to pinpoint. I wish Anakin had that accent too, but then again I wish so many things, starting with Anakin being portrayed like they're doing in Clone Wars, and the plotline being written well instead of horribly, etc. 
