agreeded with the wider tire. another thing when you air down its even wider. wider is better in my opinion. even if I go with the 13.5 ill be good .Slightly more likely, but that shouldn't be a decision maker. If you're wheeling trails where you might flop, you probably want 12.5" tires.
It's a trade off either way. Either better for rocks with a wider tire, or better for street with a narrow tire.