I reckon the marigold (unless gold farming in last stand of course)

And the chomper, I rarely use it but it's quite useful in Bobsled Bonanza because they can chomp Zombonis and Zombie bobsled teams whole, mwahahahah >:3

And I rarely use basic weapons like peashooters and cabbage pults anymore... for simple levels I use a kernel-pult and snow pea combination, and for harder ones I use kernel-pult/winter melon. Or sometimes repeaters.