Is it better to use Gatling Peas or Fume Shrooms for Endless Survival?

When playing Endless Survival, Gatling peas are sub-par compared to any AoE due to the enemy clumping up. But even then, Fume shrooms are not the way to go.

Some basic tips for Endless:

Cattails are the best, simple due to their high damage and ability to shoot anything, make sure your pool area is only them and possibly tallnuts/fumeshrooms on the first two rows. (so you won't have to have any plants defending the back)

After that come the Melons, Melonpults deal an insane amount of damage to anything due to their AoE bursts. No single line shooter (except for the Cattails) can do better. And if you want you can give each line 1 frost upgrade for the AoE slow effect.

The last important damager you place on the third row from the end (or second row from the end in pools) and it's the fume shroom. Why? it is still able to hit any target around it even if it's still chewing on the plant on front of it... place a Tallnut with pumpkin in front of your fume shroom and it can safely attack those.

Lastly, spikey grass on the very first lane to deal damage while they are chewing on the pumpkins and to take care of Zombonies.

Additionally, umbrella leaves should be spread out more, never less then 2 spots between them otherwise you are wasting coverage.

As A.bakker noted, AoE plants are almost always better in Endless, and Fume Shrooms > Gatling Peas.

Single-target damage is very insufficient late game for dealing with the huge numbers of zombies, and AoE plants then will deal overall much more damage, even accounting for the small AoE given by Torchwoods. For this reason, a Melon-pult is considerably more effective than a Gaitling Plant for dealing damage further down the lane, with a Winter Melon being even better because of the frost effect.

The only single-target damaging plant I would recommend is Cattail. This is mostly because they pop Balloon Zombies, but also because they can attack anywhere on the map, specifically covering for thrown Imps and Diggers, and dealing enough damage (equal to a Repeater) to deal with their low HP. Some successful strategies have none, some have one or a few, very few have large numbers (or the entire pool of Cattails), though at least one is required if you don't want to use Blovers or explosives.

Fumeshrooms can cover Diggers and Imps generally more efficiently if placed near the back due to their higher damage, AoE, and less lag (Cattails projectiles have a relatively delay in reaching the target compared to other plants). They are more useful in builds without Cob-Cannons, as there is a greater reliance on immediate AoE damage.