on a 6.5" wheel? 225's.
Thats it.
Conservative.
I run 245/50/16. - But they're a little bit fat for the rim. 235/55 is probably as wide as you should go on stock 6.5" width
the best choice is the stock size. traction won't really be improved with any wider tires than that because of the way they end up cupping and transferring under load.