ICG also offers a discount to CT members and I'll repeat that I think they are the most accurate of the top 4 (CAC is still too new to the slabbing world to judge yet )
For many years, I have been a big fan of both NGC and PCGS. They have been very kind to me. This changed a while back. When I started selling parts of my collection at Great Collections, I used the Market place here and at NGC and PCGS to advertise my listings. All was good until NGC told me that I could not show any PCGS coins on their Market place forum and they were not very nice about it. No problem. I just quit using the NGC Market place. I was not trying to harm them in anyway. I was just selling coins in several brands of plastic.