Potato

Requires an average of 5 mL per plant per minute and matures in as little as 90-100 minutes under lights.
Produces between 10-12 potatoes per plant under optimum conditions, and as many as 16 with the right genetics.
Optimum water level for planters is between 4000-8000 mL for the large boxes.
Stacks up to 20 per slot.

While potatoes do give the best calories, if you're going to grow something in you're farm base, make it pumpkins still. For a sacrifice of 20 calories you get 4 more healing over-time. And in the heat of battle, having a stack of pumpkins can be more useful then potatoes.

Potatoes spawn in the dark green areas of the forest biome. Credit to rustmaps.com.

While a single potato is not as good as a pumpkin, a potato plant's yield is a lot more than a pumpkin plant. Thus, if you plan to make a farm base for food potatoes is the way to go.