Bigger as in wider or taller???...
Taller = Looks, Better Highway MPG - Lower Bottom end MPG, and slight loss of torque, Loss of handling if not a truck rated tire LT vs P
Wider= Better traction, Better handling - Cost
Taller and wider = all of above....
Personally on a stock riding vehicle I allways go Wider when i can and change the aspect ratio so it is the same as the stock height..
Todd Z