Bigger = better. Period. It doesn't matter what you get, buy the biggest battery you can physically cram in there.
Of the three trucks I'm currently running:
1. '93 has 2 stock-style Motorcraft batteries, at least 6 years old. One is a little weaker than the other, but either will start the truck by itself.
2. '92 has 2 Group 31 batteries; not sure what brand. Both are different, both were 'acquired' at the local dump, both are older(at least 5 years old), and either will start it up just fine.
3. '88 has 1 Group 31 that's 3-4 years old from Carquest, and one is a smaller "advanced category" Carquest battery I got a year or two later as a spare.
Each will start it, but it cranks faster with both. Starter is getting weak on this truck.
I've also got a Walmart battery(not sure on the group, similar in size and the biggest they had one day when I needed one). That's 3-ish years old now, and starts my mom's '02 Powerstroke by itself for a couple of years...
Also had a couple of Les Schwab batteries work for years, do well enough. I thought they were getting weak, but they tested out OK in another truck.