the main thing why shamans are liked in PvP is that in a totem farm you are somewhat like a fortress. Unable to be cc'd much and pewpewpew. Bg's mainly. worked in Arena in TBC too, however due to the massive increase in AoE and DPS, it's not that easy in PvP anymore where mobility comes into play again, however, play your cards right that's too possible with shamans still. Instant ghost wolf, etc.

Why shamans? Tremor totem. If you're feared as a multiboxer, it's pretty much always game over. Tremor Totems is one of the most reliable means to counter this.

That said tho, there are other options. But with any set up it usually relies heavily on the same tactic (ie. teams can learn and counter you after beating them once or twice first). Only few set ups have enough diversity to keep them guessing imo, and shamans is one of those set ups. :P

Are shamans still the best in arena? Most likely yes. But, as opposed to TBC where shamans were the only thing that worked in arena, there are other classes with some great potential as well now. Time and multiboxing pioneers will tell. :>