WvG, if you desire a very slim and cropped cut, like interesting fabrics and MOP buttons. That is, if you want to shell out the initial cash to become a member, where you are basically locked in to buy a few shirts with a discount. The discount really just brings the shirt to the normal price. I can't imagine anyone buying it at full retail and that's sort of the point. The construction of the actual shirt isn't as good as GBV.
As for GBV, GB has been around forever, but the vintage line is fairly new. They basically took the shirt and refined the cut to be more modern (slim), but they still retained the box pleat for movement, but it causes the back to be billow, which is undesirable. So they went only 1/2 way on the slimness. Also, they retained the white or chalk buttons because, as they put it, "they're cheap!" and clearly they have a lot of them. The fabrics are really top notch. It's really the shining star of the line. They have the ability to source interesting and nice fabrics. It's the vintage part of it. They will go into their archives and pick a year and look at all the fabrics and use that as a springboard for each season. Although other companies are catching up and are able to source similar fabrics nowadays.
I've owned several WvG shirts and 10+ GBV shirts. Sold a lot of them over time, kept a few of my favorites. Just my opinion on these brands, no dog in the race, as I am very doubtful I will buy any shirts from either brand ever again.