Best I've been to with the Villa is Fulham, wonderful day out, nice part of town and a lovely grand old stadium. Best non-league I've been to with the Boro' is probably Hinckley, cos their food is just immense. Rushden & Diamonds was like going to a different planet at the time they were still non-league.
Worst, I would probably say Cov. It is the definition of a soulless bowl, but what makes it worse, is that it isn't even their soulless bowl. I really enjoy going to any away grounds really though, just for the trip and the banter