I have both -- well, my carryall isn't a King Kutter, but they're all pretty much the same.
If it came down to one or the other, I would pick the pallet forks. If you check out a couple of threads here on TBN, you'll find dozens of great ideas for things you can do with and/or to a carryall. You can make any or all of the "carryall" modifications to various pallets, and then pick them up with your forks. You just need a ready supply of quality pallets and a little ingenuity.
I have a water barrel strapped to my carryall that hasn't been off in months. It could just as easily have been strapped to a pallet and I'd probably use it more if it were.
I have pallet forks for me FEL, too, but the increased capacity of the 3pt makes the rear forks my tool of choice for the big jobs. For instance. I put a light weight steel frame that goes up about 5 feet on 4 Euro-pallets. That gives me 50 cubic feet (just under half a cord) of firewood on each pallet. Once it is stacked, I never touch it by hand again until it is going into the Buck stove. The FEL on my 4410 will just barely pick the pallets up, and even with a
ballast box, rear traction is a little dicey. The rear forks pick them up without notice and weight distribution is apparently much better, since I notice no lightness in my front end at all.