The Fernandina road store has all of the typical "gun store" products (guns, ammo, safes, shooting accessories...) and an 18 lane indoor range. They also have a hunting/archery section well-stocked with hunting and archery accessories. They also have a fishing store, called the "Fishing Outpost" on the premises as well. Hands down the best fishing store in town.
The Farrow road store (someone called it the warehouse store but their warehouse hasn't been there for a few of years now) is a much smaller (around 1000sq ft) store and is more inline with your typical "gun store." They carry guns, ammo, and shooting accessories.
The staffs in both stores are good. The Fernandina store is typically considerably busier (makes sense given how much more they offer to a broader customer base) than the Farrow Rd store. The Fernandina store is a little easier to get to from the highway, especially if you've never been to the Farrow rd store.
I shop at both stores but since I also hunt and fish, I spend more time at the Fernandina store. That said, I won't shop anywhere in Columbia other than PSA. Between the two stores, they have what I'm looking for at better, or at the very least comparable, prices than anyone in town and both stores have knowledgeable staffs.