I like to use Tangrowth, actually. Give it Sunny Day, Ingrain, Leech Seed, and toxic, leftovers, and an impish nature.
If you are able to set up, you will be able to be gaining back health 4 times every turn, while your opponent takes damage from leech seed and toxic. Tangrowth already has decent Def. and Spec. Def. stats as it is, too.