Cheddar has some of the best local quality, it's only 45 min or so from Bristol but to the south, so presumably not on your way home.
I agree Ban-y-gor is one of the nicest venues in the area at that grade range, both in quality and setting.
The quarry at Wintours is worthwhile and easy/accessible.
If you're happy to do trad then Sea Walls at Avon is better than it's polished reputation (IMO), you'd have a fun session there on the classics.
Enjoy and let us know what you end up doing!