Stockycub is right, that the Hoist will be more active.

XXL Xtreme (or however you spell it) is a larger space than the Hoist and has either about the same or somewhat fewer fellows in attendence on Fridays; but because the space is bigger it appears less busy. If you are more interested in bears, then Xtreme will be a better bet. But if you have the gear to make dresscode, then a trip to the Hoist is stimulating. There are also other good options in Vauxhall near the Hoist.

The Hoist has a somewhat more restrictive dresscode than Xtreme but not as restrictive as the Backstreet or Club Hardon.

That said, Friday nights are the busiest night of the week at the Kings Arms, mentioned above. So I would strongly encourage you to at least start your evening there.