The 315/30/18 would be horrible on the street in my opinion, not enough sidewall and you will go through aluminum rims regularly unless you go forged. The 295/35/18 has the highest sidewall at 4.1 inches and will give the best ride and rim protection, it's also the tallest tire and should help gas mileage due to highest "gearing" 772 revolutions per mile. My 2 cents says comfort and rim protection is worth losing 3/4 inch in width on 12" wide tires.