ice shard will deal more dmg
but powder snow will generate energy more quickly by like 50% more quickly
both are almost the same in terms of speed cast, honestly with a two bar like avalanche wont really matter, the best use of faster energy gain comes when you are using a 1 bar skill like blizzard
you cant go wrong with any of both unless you really want that faster gain energy then go powder snow if you want more damage then is ice shard
