I have flown PE & WT+ several times to the US (east and west coasts) and to be honest there isn't a huge difference.
Fundamentally you are getting a bigger seat and a bit more room than Y.
I think VS give you a better service than BA. BA food is generally better than VS. Both will give you more drinks if you ask. IFE depends on the specific plane, but at the minimum is OK.
And surprisingly enough, the costs are usually the same.
So I would base the choice on (a) schedules (if the timings are important), and (b) if you need the miles on that airline for a particular reason.
As has been said, either is a lot better than Y, and the extra cost is usually not too high.