OK, I have to ask. Why the 18 and not the 22?
I want to buy one this spring and have been asking the question myself. It is just me and my wife. Have a couple of smokers and grills.
But knowing my personality if I buy the 18 I will be wondering if I should have bought the 22.
I'm tempted by the 22, but merely so I can put a full rack of babybacks on it without futzing around. BUT, my wife and I are now empty nesters and she doesn't eat red meat ...when I make ribs, or pork, or ham, or brisket etc ...I'm the only one eating it (dinner and lunches at work). Chicken (and poultry sausages) are the only thing that she eats out of the smoker ....and loves that stuff, but for 50% of my smokes, I'm only feeding a single person. The other half of the time, only 2 people. Once in a blue moon, we may have another couple over for dinner. Even though I may have to cut a rack of ribs in two (or futz with them and put them over a foil-covered brick or pipe or something), the 18.5 still has the capacity to blow us out of the water... and is big enough to make it easy to run, unlike the little (finicky?) 14. So ...I can't justify the bigger size or the higher rate of charcoal usage for us. If I bought a 22, I'd buy the charcoal bin/gizmo for an 18 and would put it into the 22. I like keeping all components engineered to work together, together. Another factor, and perhaps the deciding factor for me, is that I can buy the 18.5 at any of several shops in town ...and for prices that are as cheap as Amazon (even with free shipping) ...the 22 would have to be shipped. I like being able to check out the box before I buy, and having a local company to go to if something's mucked up... with Weber's great support as the back-up.
So, there ya have it... empty nesters who don't need a lot of capacity in their smoker. If my wife ate red meat and/or we had other mouths to feed, then I wouldn't hesitate to get the 22. Can't go wrong either way.