You really have not given enough information to allow us to provide meaningful input. For example, most traditional Peapods were intended to primarily be rowed. Those that had a sailing rig did not have a centerboard and relied on a 'plank keel' which is simply a deeper external keel timber. Because of that, they did not sail well to windward no matter what sail plan you put on them. You rowed to windward and reached or ran under sail.
But once you add a centerboard, these are pretty efficient sailing hulls and should be able to sail pretty well on all points of sail.
So, then the question becomes how do you plan to use the boat, and does the design include a centerboard. If you plan to row more than sail the boat, a spritsail is a nice rig since it is quick to rig and quick to stow, and frankly was probably the original sailing rig if the boat had a sailing rig at all. It sails pretty well on a reach or a run and so work well with a plank keel.
A lug rig does not sail as well as a sprit rig and is prone to excitation roll when running down wind like a spinnaker and makes for a rolly ride. It also tends not point as high as sprit rig and can be higher maintenance since there tends to be a lot of chafe.
A gaff rig will generally point slightly higher than either of those two and will reach and run similarly, but the spars tend to be harder to stow in the boat when you want to row since the gaff is captive on the mast.
If the boat is one of the lighter weight, stitch-and-glue interpretations of a Peapod and has a decent centerboard and rudder design, I personally would do a sliding gunter rig which should out perform all of these, but will need you to hike more or reef sooner in a stiff breeze. I have generally concluded that sliding gunter rig can be designed to stow easier than a gaff rig.
If the original design is lug, balanced or standing, the mast location including partners and other structural members will be forward of the location for a gaff rig. The lug may or may not have an unstayed mast, the gaff probably will have a stayed mast and forestay with headsail.
I did want to respectfully mention that this is backward for a gaff vs lug cat rig. The position of the mast on a cat rigged gaff rig would need to be farther forward than that of a cat rigged lug rig since part of the lug sail is forward of the mast on a lug rig. But if a headsail is added then the rig would need to move aft. At that point, the sliding gunter rig would be a no-brainer.