I personally think plants are stronger. Zombies are op against beginners mostly because they dont know what cards can be inside of tombstones at all and or weed spray demolishes everything they have. I suggest playing zombies in the early ranks with weed spray up to 15/20. I usually see control/healing plant decks succeeding the most in my experience using and against them...If you're going aggressive with plants try using as many as possible with 3 or more attack to avoid weed sprays and carry around alot of buffs.