I'd just like to throw my two cents into the fray because I needed to vent about this lol.
I recently had a handful of books graded by CGC, and a handful of books graded by PGX. Let me just say, CGC's customer service is atrocious. I mean beyond poor. I will
NEVER do business with them again, nor will I buy a book graded by them. My friend and I sent out 6 modern day comics for regular grading on
June 21. This service is supposed to take 20 business days (1 month). Do you know how long it was until we got our comics back?
DECEMBER (120 business days, 6 months)

!! Their communication/explanation for the delay? Vague references (to the comic shop we did it through) of backups due to comic con and losing some graders to the competition (PGX). So for 6 months, we were completely in the dark as to the status of our comics.
On the other hand, we recently sent out 12 modern comics to PGX. PGX sent us an email upon their receipt of the books (1 week after we shipped them), along with their estimated date that they'd be done by. They then sent out an email when the books actually did ship (7 business days after the first email) along with the tracking number. And, oh by the way, they beat their own estimated finish date by a week. They certainly did an excellent job with communication and kept us informed every step of the way.
As for prices, again, it wasn't really close. With shipping and the broker fee we had to pay the comic shop, CGC ended up being about $30 a book to grade. With all costs included for PGX, it ended up being about $15 per book.
As for the quality of the grading. I think they're pretty much the same in my opinion. Especially considering CGC has lost a few graders to PGX, I imagine the difference is only due to reputation due to CGC's long foothold in the business. In my opinion, even
IF CGC was marginally better at grading, the vast difference between the two companies in customer service and price would still make me use PGX again over CGC in a heartbeat.