Originally Posted by Wade
22". The 18" is fine for most things but quite quickly you will wish you had gone for the 22"
I bought a 18" back in 2005 well before the 22" was available. I can't bring myself to discard the 18" and move to a 22", but having a choice I would say go with the 22" now. Yes the 18" is more fuel stingy as you are working with a smaller air volume, and yes the 18" will run longer without refueling the fire ring, but is that really an issue? Charcoal is cheap and the WSM is consistent so once you figure out the 22" will run X hours on a long smoke you know when to refuel (assuming it's a really long smoke and a refuel is needed). The main food advantage is the 22" will handle full racks of ribs and brisket without either having to cut them to shorter lengths or roll them or perform some other feat to make them fit due to length. Both the 18" and 22" will make wonderful smoked food and the 18" can hold a lot of meat without modification. I regularly do 4 10 pound butts on my 18" for the office. I have done 6 in the 18" one time. It worked, but I don't think I want to repeat that as it was pushing the capability of the 18" a little too much. I had to do a lot of meat rotation and stand them on end like tripods on each grate. I've seen posts of 6 in the 22" no problem, so again if you need volume, the 22" is clearly the way to go.
On the flip side, now that both my kids have moved out and it's just the wife and I, the 18" is plenty big for what I need. I can adapt ribs and brisket to fit. So depending on the size of the cooks your will likely be going the 18" may work better for you. You save money up front and on fuel. I do pulled pork, sausage and snack sticks mostly in mine and occasionally do ribs. I infrequently will do a small brisket so this explains why I see no reason to discard my 18" and move to the 22".
And like Richie said, add a BBQ Guru (or similar) to either WSM and you have about as close to set and forget as can be done with charcoal and fire.
And you can add an e-WSM mod to either by buying an extra door for the body so you can run low temps for sausage and snack sticks as an electric smoker just by switching out the body door. To go back to charcoal, just put in the other door and smoke on.....