In reply to Ardverikie: I've been climbing in London for 3 years now and have been to a lot of the walls. My negatives in terms of BOULDERING:
Arch: gets busy, hot and very chalky air.
Castle: I suspect this is your 'random jugs on wall'. I once saw a V1 there that was a line of about 6 jugs, perfectly verticle, perfectly orientated for L-R-L-R-L-finish. Unbelievably lazy. Other than that busy, only good quality on V4+, pretty hard grading.
Westway: Bouldering at the back is NAILS (at least last time I was there). Was struggling on routes 4 grades below what I climb regularly at Arch. Also, why go to Westway to boulder with the awesome lead wall
MileEnd: Secret Garden is outside (under a tent) so dont go in cold/wet weather unless you like realism. training rooms are really small, indoor bouldering walls are VERY high (nearly equivalent to downstairs rope climbing walls at Castle).
Reach: AMAZING training room with Bose soundsystem, but if we're talking negatives... they've had a hanging boulder set by Johnny Dawes that has been cordoned off since they opened because of no mats. So you can't climb it.
I haven't been to WestOne or Brixton.
See here:
http://www.kclmc.org/walls-in-london M