@agentevil007 why should he be on that list? Petrified Cacti is pretty good actually, slow shot but decent DMG and good splash, 150 life more life than the normal cactis, in close range I still prefer bandid cacti but petri is also an option. The worst cacti for me is the ice cacti, no DMG, long reload time, no freeze at all, the only good thing is more ammo but in general ice cacti is one of the weakest plants.
For me the worst is Rose, all of them! Most of them are extremly strong, normal rose and druid rose do massiv dmg, but I hate playing them and playing against them. Spam abilities, auto aim, immortality, this character is just not fun at all in any point. Just holding the left mouse button, thats all you have to do since end of the beta. This character also has the most annoying special in the game: goatify. When you get goatified in close range you are 90% dead. Its probably because I love close range challenges, scientist and chomper are my favs in GW1 but now no just no. With rose you just have to goatify someone, then the stun, after that the match is over...whohoooo! In strengh, ice rose is pretty much the weakest, low ammo, you have to click, long charging time, freez is almost as bad as ice cacti (I dont have the ice upgrade for her).
The worst zombie is party brainz, theres nothing to say about him, he is just bad. Then its Tank commander, yes I loved him back in GW1, but now hes not that good at all. He got nerfed for no reason, the maps are wide open, a single shot is not helpful even with those 2 reload upgrades. You still can play him, but hes bad at capturing the garden, bad at bombing areas and bad in close range, any pea, citron, corn, rose, chomper can overwhelm him easy.