I use the "big 4" buying groups and am happy to share my honest opinion of them after 1+ year of using them all. Keep in mind I only do the Amazon deals with the exception of consoles that I have shipped to home before throwing a label on a box and shipping it out to the buying group (since that is still profitable).

BFMR: Lot of people say they are the best, and I'd agree to an extent. The fact that they do same-day scan-ins and next day payouts is amazing and really takes a lot of the hassle out of the reselling game. They don't have quite as many deals as the next BG I'll discuss, but anytime the price is the exact same for an item across all BGs, I'll almost always choose BFMR simply due to the fact that I'll be paid out the quickest for it. Like many BGs, BFMR is trending towards more of a below cost Amazon deal place with a few exceptions.

TDB: They started incredibly strong as a new BG in 2021 but have now grown to a point where they are a bit slower on scan-ins and payouts then what made them great in the beginning. However, they are still leagues better than MYS and PM. TDB by far has the most deals (even more than BFMR) and if you are a member of their discord, you can usually compare rates between their website and the discord and open tickets to get price matches. It is a hassle sure, but it's an option no other BGs offer. They also issue free labels for consoles, so they are my sole recipient of consoles when I get them. They have multiple areas across the country that you can ship your consoles too, and these are typically same-day scan-ins. Shipping to their oregon warehouse is still backlogged and takes a few days, probably because of how popular they've got (Assuming they are taking business away from MYS and PM). They also rarely offer below-cost deals and always seem to try and do their best to offer at-cost prices, which I appreciate. They also offer ACH.

MYS: Probably the worst of the bunch, however as of late they have been posting the most deals (even if they below cost) such as Apple Watches and iPads. There are ways to still be profitable with below cost deals, but the whole point is to make money, so anytime the BG decides to scrape 2% off the top for themselves, it makes me annoyed. I also hate encouraging that behavior by shipping them below cost deals, but sometimes you have spend to meet quickly. I probably shipped the most to them in January compared to the other groups. They were seemingly scanning in within 3 days or so, but they appear to have fallen off the past few days. Their December was awful though--probably went 3+ weeks to scan in after Black Friday and another 2+ weeks to receive your check.

PM: Pretty identical to MYS except their deals have been nonexistent as of late. They do offer ACH, which MYS doesn't, so at least there's that, but payout requests since Black Friday have easily been 2+ weeks.