Let’s review the critical criteria.

SOUND QUALITY
1-10 (base on general opinions I have heard over the years and my personal bias)

Studer 8-10
Ampex 8-10
Otari MTR 90 8-9
3M 8-10
MCI 6-8

RELIABLITY
Studer 7-9
Ampex 5-8
Otari MTR 90 8-9
3M 6-8
MCI 7-9

PARTS AVAILABILITY
Studer 9
Ampex 6
Otari MTR 90 8-9
3M 9
MCI 10

TECHNICIANS
Studer 7
Ampex 2
Otari MTR 90 8-9
3m 3
MCI 8

This is what I am now referring to as V-U.S.E.D rating.
VINTAGE USER SATISFACTION ELATION DYNAMIC

Hope that helps. My best advice before you buy anything is find the/a guy who will be your Personal Tech.  Investigate the tech first. Vet him thoroughly for reliability.

Once you have a good technician, hire him to help you find a good machine. Let him “own it” with you so to speak. Then when you find one he can check it out with you. Paying a little extra now is better than mountains of regret later.

Story #1. I have a client who insists on buying a Studer. I told him buy a 3M 79. I could find him a good one and when it needs love, I already invested may miles learning it so i will save him tons of time and $ making it good. I did say “they all go bad from time to time” didn’t i?

He goes and gets “a deal” on a Studer A820. Now it’s going to cost him a fortune to repair because I know very little about the specifics of Studer and he will have to pay for me to go to Studer School on his dime (or find another tech).

So dig in and enjoy, ask questions, make comments and send info.