I think Hugh’s right on venues, but as a guide Mondays and Thursdays are the most popular nights with dancers (as opposed to Tuesdays in Cuba, which is most popular with fag-smoking drunks). Mondays is the better venue but John’s choice in music is an acquired taste: some nights it’s fine, some nights it’s seriously dodgy. The Toad has better music in my opinion, and goes on later, but can get too crowded. Monday nights has the advantage that it only has dancers there, while Thursday gets drunks wandering around on occasions.
Asking us to nominate the best dancers is a bit invidious. In addition to Hugh’s guidelines, I’d suggest checking that people are actually dancing on the beat. One major cause of flailing arms and striding steps is when the man has no sense of rhythm so leads the woman by force.