I've owned at 18.5" WSM since 2005 (old style). The only thing a 22" will do that an 18" will not is you can lay full length racks of ribs and brisket on the 22" grate. On the 18" you either have to trim into multiple pieces, roll or tie them to compact the size a little. And the other obvious thing is the grate is basically larger so you can put more food (ie, chicken wings, chicken, sausage, etc...) on a grate. It also depends on how big a family you cook for as to which one you might need. If there are only 2 to 4 of you, then you will probably be burning more fuel to cook the same amount of meat in a 22" vs one of the smaller ones. The smaller the pit, the more efficient it seems to be IMO, but I've never used a 14".