+1 for the Acorn. It is just too versatile. Smoke, grill, pizza. It can do it all and do it well. I have a WSM and it certainly has more capacity than the Acorn but if I was going to chose one and only one it would be the Acorn.
Weber 22.5 WSM (2) UDS, Chargriller Acorn, Pit Barrel Cooker, Pitmaker Vault, Safe and Sniper on Trailer