I still like mastery for PvE and PvP. I run with a separate healer toon for PvP so don't rely on shammy heals generally, although if you do, then I acknowledge haste will have an advantage in this aspect.

What I like about mastery is that 1% mastery will mean your nukes (not including ES/fulmination) will hit 1.5% harder on average. Getting kills in PvP is all about having heavy nukes and this is the best stat to achieve this. 1% Crit will only give an extra 1% to nukes (not including LvB). Sure haste will let you get more spells of in a short period of time, but this is only if you are allowed to stand still and cast. Even if this is the case, again you will only increase your total output by 1% per point of haste rather than the approx 1.35% from mastery (averaging damage from spells affected by mastery x 1.5%).