What are the pros/cons of both? Thinking of utilizing my stock wheels which would limit me to 12.5" but is there an incentive to ditch the stock wheels and to be able to go with 13.5"s other than looks? Pics of both?
The stock wheel width is out of spec for both 12.5 and 13.5. Some people still do it with the 12.5. Many shops won't mount them though.
As for widths it depends on where you drive and the purpose. On road, wider tires tend to roam more and follow lines/cracks in the road. They are also worse in winter conditions.