After I moved from a kettle, had a 18" WSM = 1995. This was the only available size at the time. Awesome cooker. However, even with company, I always thought it was bigger than needed, for most of my cooks. I'd normally cook for 20 people or so. The key question is what you like to cook and how many times will you do it? First off, ribs are not the easiest cook to do all at once for a bunch of guests, if you only do it occasionally. Cooking real time I mean = a lot of work. If I intended to have a lot of people for ribs. frankly I'd cook and foil them ahead of time, then just warm them up. Cook something easy on the smoker, or appetizers on whatever grill you have. Good ribs are good ribs and will let you enjoy your company and reduce the workload. My .02c I never had a 22", but understand the coal use is exponential compared to it's smaller siblings.
Dave
Dave