In my opinion it really doesnt matter, due to them being so close in size. When you convert that size to the english language you get 225/75/16=29.28in and the 235/70/16=28.95in (hopefully my math is right). But as you can tell the size difference is minimal and wouldnt affect speedometer and the revs per mile a whole lot. What I would do is go to the tire store and compare prices between the two and also what they have in stock. I know when we threw new tires on our jeep we were going to stick with stock size but they didnt have them in stock (235/65/17) but they did have 245/65/17 which is about an half inch difference in diameter. Hope this all makes sense and helps you in your decision.
03 WJ Limited, 4.7L, Quadra-drive, Firestone Destination A/T (245/65/17), Run Valvoline Max Life 10W-30, More to come
"Dont tread on me is what it says and I'll take that to my grave..."
~RIP 87 YJ~