In reply to Michael Gordon:
> I don't mind which recognised knot they use, but I would hope in this situation someone would lower a screwgate attached to it so I could just clip in, rather than having to try tie-ing in whilst hanging on for dear life.
They might not if they're wall-trained, because they'll have been taught that clipping on to a harness with a krab is "wrong".
Doesn't have to be a screwgate by the way. If you're hanging on screaming for a top-rope you want the quickest clip-on available. Screwgates can work themselves locked as they jiggle down the crag.
I'm a bowline man. Started with it, changed to Fo8/Karabiner/waist belt after a few years, back to bowline, then re-thread Fo8, and have now returned to the bowline, albeit one of the new ones described in Mark Gommers' excellent paper "An Analysis of Bowlines". Look it up.