BA Pro's

Better seat and lighting
Better food and drink (VS is uniformly awful, poor quality, small portions and poor wine selection)
Better crew (a very good VS crew is a rare thing, as is a bad BA crew)

VS Pro's

LHR Clubhouse (arguably the best lounge in the world)
Check in at LHR (even without the limo service, very impressive)
Marginally better AVOD
Better bed
Pre-allocate seats

IMO the bar area on VS is a disaster. It attracts once a year travellers intent on having a good time. This is crap if you want a quiet flight or a good nights sleep. T5 Galleries are pretty good by global standards but are a LONG way behind the Clubhouse.

Think about miles too. Flying Club isn't a great FFP, whereas the BA miles earned from your trip would get you 2/3 of the way towards an MFU. Sign up for the BA credit card in the US et voila.

Personally? BA every time. I just don't like the style over substance approach of VS and have had too many bad experiences.