I have several of both,
The 22 uses a lot more charcoal and I like the 18 inch ones because I can put several in my truck and not have to take my tonneau cover off. The middle section is about 3 inches too tall to be able to transport it without taking my tonneau cover off.
Get or make a small ring like others said and you will save yourself a lot of money in charcoal.
(4) 18.5" WSMs
Weber OTG 26.75"
Worlds Fastest "Green" Thermapen
"Not a competition cook, just a guy who loves eating and cooking Q."