For myself, I can immediately say that I think the worst is the shadow priest. (Of course, I also play a shadow priest...) Perhaps it is simply because there are some especially wily shadow priests on my server, but they give me fits in battlegrounds. The best to PvP against - that is, the easiest to defeat - is more difficult to pick out. There are specific warriors that I have trouble with (charging, intercepting, breaking fear, striking for huge amounts of damage - and killing me in two or three hits), but others I find to be complete pushovers (quickly taken down in the course of a single psychic scream). Rogues are also hit and miss in my experience - if they don't manage to take me down from stealth, during that initial stun, I can almost always cope with them. All healing classes are annoying, due to their potential longevity (though paladins, of course, are the worst), and I have no strong feelings one way or another on the remaining classes. But what about you? In your experience PvP-ing, what's the best and worst class to find yourself up against?