The standard gauge has usually been 18, with 16 becoming more popular. I dont have any cons with the 12, I am assuming in your case it may have something to do with the design of the sink (which is nice looking). Most folks are fine with the 18.

The 12 you are looking at is heavier than most folks would need, but their is nothing "wrong" with it. If it is extra large or something about the design requires greater strength, that may be what it needs to be. It will be heavier, and that might mean you need to check your mounting and support for it to make sure it will hold the sink weight plus water, pots and dishes.

My main sink is a large single bowl (31") and is 16 gauge -- the prep sink is about half that and 18 gauge. Neither has given me any concern and from all I've read and encountered, I couldn't say you need anything heavier than those. Is there a reason you feel you need something extra heavy?