Based on my experiences on the LHR-SFO routes which I've flown more often than I care to recall, my ranking, best to worst, is:
BA business - wonderful
VS upper class - also wonderful but seat less comfortable & less private
BA WT+ - very good
VS premium economy - also v. good but again, seat less comfortable than BA
AA economy, best economy seat but no direct flight
BA economy - if you must
VS economy - if you really must
UA economy - yuck, really yuck!
I did get upgraded to BA first once. The best flight experience ever, or buy a new car.
My own opinion from actual experience, others may differ! Based on leg room, comfort of seat in general, & overall 'lack of hassle' experience. I don't rate TV screens or free drinks very high; give me a good book & the space to read it & sleep.