Disc priest since pretty much always, decent dmg decent CC decent survival and good in many comps, bonus is that they are also hard to master and reward skill alot more then the other healers.
This from my retail experience and to a lesser extent from Blackrock.
Only downside is that they cant be stacked effectively in raids so you will find yourself somewhat limited in that aspect.
all of this "google is ur frend :D".. so we are on a forum and it is blasphemy to discuss stuff that is related to the theme of the forum???
and yes, discuss, since what is "best" is subjective.
anyway:
>what healer class works best in pvp?
all of them work well
>and which one has the most agressive playstyle?
discipline priest and shaman, with disc being the more aggressive one of the 2