I've tried both Major Gains and Vector 8 weeks.
Strength gains were the same from both, nothing special, except Vector made me bloat horribly and added greatly increased hunger which is already a problem for me.
Vector turnt out to be just a bunch of a hype unless you stacked it with Follidrone, which I don't see why you codulnt stack FD with many other bulkers.
Would take Major Gains if I had to choose.
Though I'd take Follidrone over either.