You should use them all too, if for no other reason than to see the animations. Others simply tweak the rules a little, limiting you to a specific set of plants, a certain amount of sun, having no more than a certain number of plants active at one time, getting through a level without losing more than X number of plants, or defeating a certain number of zombies within a set period of time.
Of course, you’ll have to adjust your tactics depending on the zombies in each level and the rules in play, meaning that while you’ll have favorites, you’ll wind up using a fair slice of the available arsenal over the course of the campaign.
