If all you can know is one of these arts, it's BJJ. But great wrestling with a working knowledge of BJJ is better than the other way around imo.
the thing is its hard to get decent wrestling training in the UK. Yeah there are olympic level wrestlers teaching in MMA gyms but they are few and far between.
Depends on the organization. UFC should be renamed UWC: Ultimate Wrestling Championships. A few takedowns and the match is yours. Pride back then was focussed more on damage done than wrestling. I think some of the other orgs are the same.
If UFC allowed knees to the head on the ground it would help wrestlers gnp a lot more though. It's hard getting a finish on the ground with 5 minute rounds as well with just punches and elbows which may not be possible if you don't have long arms. Coleman-Igor anyone :hey
for defense bjj, for offense wrestling... fighters need solid defense first and foremost so logically its bjj however once your bjj is at a certain standard wrestling should then take priority.