What is the highest DPS plant?

Cob Cannon would have the highest DPS then. Once the corn cob is produced, the player can click on the Cob Cannon and can manually launch the corn cob onto an area that the player targets. The corn cob will explode and deal 1800 damage to all zombies in a 3x3 area, like the Cherry Bomb.

I think Melon Pult's answer is the way to go. Do consider also that for masses of zombies coming onto you (in Survival and Last Stand), splash or area damage may cause a weak plant to be dealing more damage than a stronger one.

The wiki says that Spikeweed will do damage to a single zombie at a rate about 4/3 that of a peashooter. A peashooter will do 20 points of damage per shot, so a Spikeweed would be doing ~26 damage per tick.

Against a single zombie, a Gatling Pea without the aid of a Torchwood will do 80 DPS, which is practically 3x the damage that a Spikeweed could do. But if you have 10 zombies stepping on it at the same time, the Spikeweed will be dishing about 260 DPS, and it will bypass screen-door shields. A Spikerock would be dealing 520 DPS total!

So you might also with to consider nerfing Spikeweed and Spikerock.

DPS is but one of many characteristics. Damage per tile moved seems more useful. If a fast-moving zombie is coming at you, DPS doesn't help much unless it kills them. But, if you can slow or stop them, then you gain time.

Another statistic is cost. The little tiny mushrooms do little damage, but they are free, and need to be eaten (most of the time) and thus will slow zombies a little.

For example, the watermelon slows enemies, thus creating more damage per tile moved. Same with the spikeweed, and other things also slow or stop them.

On levels with a lot of zombies, plants that can damage more than one zombie gain more use.

Depending on which PvZ game, Hypnoshroom can do the most damage, if it gets eaten by a powerful zombie.

Damage per:

1. second
2. tile
3. cost
4. total zombies on the board
5. slow, insta-kill, etc...