Thomas is the easy choice if it is based on their current contracts.
This seems important to take into account - kind of like the Carroll vs. Crowder debate. Unless you believe Jackson is going to reach top 3-5 PG status, then they both belong in the same tier. I think you also have to like IT's ability to deal with being switched back and forth to the bench - very few players could suck it up and still play as hard / efficiently as he has with the Cs. He remains a team leader.