Short answer – Lusso ProGel (£50 and made in the UK).
I’ve got various lycra bibshorts, made by Assos, Endura, DHB, Impsport etc..and although they’re all comfy, each creates its own problem if I do a really long ride, for example, chafing in a certain place.
The one pair of shorts that I can rely on for long rides are these from Lusso:
http://www.chainreactioncycles.com/lusso-progel-bibshorts-ss16/rp-prod130485
As an example of how well they fit me, I did all of Mayhem (18 laps) wearing them. I find the padding is very generous around the ‘seat bones’ and nicely cut down in the middle section, as opposed to the bulk you get with Assos shorts.