Personally, I prefer BGS for modern cards mainly because I like the slab the best, but PSA is just as good. The only real big difference is a BGS 10 is a higher grade than a PSA 10. A PSA 10 is equal to a BGS 9.5. Having said that, there is almost zero chance you will get a BGS 10, so it isn't really something you should be thinking about. For vintage cards, PSA = BVG = SGC as far as I'm concerned.
TL;DR: you really can't go wrong with either PSA or BGS.
TL;DR: you really can't go wrong with either PSA or BGS.