I have only ever played in the fox which is now closed. I did try to play cash at the empire but there was a waiting list so I went and got drunk instead.
As people have said here the empire seems to be the sofest game, but I think for more variety the vic would be a good place to check out, as they have games running around the clock.
1-1 NLH, 1-2 NLH, 2-5 NLH 2-5 PLO 5-10 PLO
I follow the vic card room on twitter and there always seems to a decent amount of tables going.
I know thats where im heading next time im in London, I also want to check out the Hippodrome, which isnt far from where the Fox club used to be