Those ratios are really pretty close together -- I'm not sure one could tell a big difference either way.
But you do want to make sure that whichever you choose has the upgraded towing goodies you will need. **disclaimer** I don't know a lot about how Fords come from the factory, or if there are options such as transmission or oil coolers that you will need to get the max tow numbers. But with GMs, the lower (numerically) gears usually mean the truck also lacks the heavy towing equipment as well.
you should make sure that the only difference between them is the axle ratio.
Good luck!