Stick with 17's. I've had experience with 17's, 18's and 20's.
20's, even on AT's run rough and they won't allow you to air down as much if you decide to take it offroad and get the itch.
18's (I currently run these): tires are more expensive than gold and they don't look any bigger than 17's. My duratracs are excellent for my DD and love the way it rides
17's (what I'm switching back to): less expensive tires, more size options, will allow for the most sidewall out of the 3 options which means more comfort and air down capability.
'14 Anvil JKU Sportis all that's in my garage.
What would I know though...I'm just crawlin' at the mall.