I have never shot anything from Copper Creek. Once things return to some semblance of normal, I will probably order some of their ammo to try out. It gets good reviews from what I've read.
I have bought several hundred rounds from Southwest (all 175LR). I have an order for 400 more rounds in right now.
I had a bone stock DPMS SASS that would eat everything I put through it EXCEPT the SW 175LR. It just wouldn't eject the stuff. I could run a mag of FGMM or Hornady match (even Winchester hunting ammo) and mix in a couple of rounds of SW175LR and it would jam almost every time it came to the SW round......there was just something about it. Get this: if I fed the rifle one round of SW175LR at a time, it would shoot 1/2" 5-shot groups all day long, so the stuff was definitely accurate.....it just wouldn't eject 80% of the time. It was frustrating as hell. You can lose confidence in a weapon really quick.
I still shoot SW ammo pretty much exclusively, just not through my gasser.
Because gassers can be a little finicky, buy a box or two of different ammos and see which one groups AND feeds best through your gun. I bought a few hundred rounds of SW175LR and found out my SASS hated it. Save yourself a bunch of hair-pulling and buy a box or two and then make your big purchase when you've found what your gun likes.