In the years you own PSA is the KING. BGS is known for grading sheet-cut cards and their value is much lower as a result. I collect PSA graded 70s and 80s hall of famer rookies...still looking for some if you have any
...and I would never dream of buying a BGS graded card.
Now for modern cards, BGS and PSA are about equal but, anything older than 1990 and PSA is the one to own.