drain clean

I'm having an issue with a clog, and just can't wrap my head around what the issue could be. My kitchen sink on my upper floor has given me trouble for quite a while. I had a 25 foot pipe snake that I could use with a drill, and stuck it in the vent pipe from the roof, and that seemed to help...

Can anyone tell me if it is more common to find a 2" copper drain plugged or a 2" PVC drain? Also, Should I just replace the copper drain pipe with PVC? Thanks!

Plumbing story of the day: Property management company called and wanted a price on unstopping a drain over the phone. As usual I told them we can'r/won't give prices over the phone without doing a diagnosis 1st. They pitched a fit and said their "normal plumber" charges $150 to unclog the main...