We are comparing an F product against a J product of course, although some of us may remember VS UC being touted as "First Class for a Business Class fare" many years ago. That might have been true to some degree twenty years ago, but certainly not now.
If I was given the choice, definitely I would choose BA First because the better personal space, the personal attention, FF earning and spending options, and the booze quality is so much better. I also find crew on BA to be more consistent than VS.
Most of my longhaul travel has shifted to BA F in recent years from VS, due to the continual penny pinching at degradation of product at VS, plus the decline and final demise of BMI (who I used to treat as "Virgin Europe" for FF accruals), and BA's larger network. Ten or twenty years ago, there were many more key differentiators between VS and other carriers, but the bean counters at VS have devalued the product to such an extent that there's less and less to choose between them and other J offerings.
What do I miss about VS? The onboard bar, the Clubhouse particularly at LHR, and the drive through checkin and private security channel at LHR.