If you're okay with the age, the 2015 Retina is actually still quite good. It doesn't have M1's all-around performance credentials, but the 15" HQ variants (all 16GB for 2014/15) still holds up against the M1 in many situations with a modular SSD, but soldered RAM. The 2014 isn't a bad machine if you already own it, but unless you're getting a good price break stick to 2015.
I still run Catalina on mine (High Sierra on SATA based), rather than Big Sur - I don't like the AirPrint requirement which is my primary objection. For 32-bit SW, that died with Mojave so that reason is throughly expired.
I realize for many the 15” rMBP is the equivalent of buying a AMG vs a Honda but if you can afford to take the AMG, BMW M or a Maserati home with you can afford both, which one would you want?