Petal Blizzard

Great moveset for attacking! But don't power it up any further: he's great both for enemy and friendly gyms. Solar Beam is slightly better but not that much.

I prefer petal blizzard by far for attacking...no more 5 seconds giving the defender free swings. I actually like it for defense as well..solar beam is so easy to dodge. Same basic reasons why Vine whip. I personally only spend dust on petal for the grasses.

I have a few grass mons I use for attacking, and I prefer petal blizzard - even though it feels like it does less damage, the shorter cooldown is really useful when trying to dodge. Also, I think solar beam is kind of wasteful - if a defender has like 15-20% HP left, I don't want to use up a full solar beam charge. This means I'll keep using quick attacks, which ends up lowering my DPS.