it depends on what you have
leaf storm is the best for mixed and special attackers
leaf blade or wood hameer for physical attackers
synthesis for a wall of some sort
overall i would say leafstorm is the best
I personally like leaf blade the best because there are no negative consequences to it (i.e. frenzy plant makes you recharge, wood hammer does recoil) and it has a high critical hit ratio (right?). Energy ball is pretty good too. Giga drain would be my favorite if it has just a little stronger.