My favourites are:
The Everyman, Saxmundham. Monthly concert club, good floor singers, gets a lot of local people in who aren't really folkies but trust Steve and Mary Dickinson to book a good night's entertainment. Everyone gets a seat, no smoking, they start strictly on time and talking while anyone's performing is distinctly frowned upon. Result: everyone feels they're getting their money's worth.

Sutton (Beds) - also a monthly club, in a village hall. Similar in many respects to The Everyman but a bit more informal.

Last Friday we had a cracking night at The Black Diamond in Birmingham. Enthusiastic, great if you like singing choruses - they certainly do! Recommended.

I'll second the mentions given to Ampthill (nice small and friendly club) and Bedford where our only visit to the new venue so far was a singers night with so many there was barely time to go round the room twice with one song each.

Norwich (Branford Arms) is good too.
Sharps! (Cecil Sharp House, Tuesdays) - how could I forget that one!

It's quite clear that everyone judges clubs by different criteria, but most of the one I've mentioned have been well attended which seems to be a good (not infallible) metric for any club.

They're all clubs rather than sessions. The Sutton people have a Friday session every month too, and my favourite all round (songs/tunes) session is the Fox at Pirton (near Hitchin) 2nd Wednesdays.

Anahata