Wow - there are "opinions" about gear? Go figure. My two cents (everyone has a pocketful) on 2" machines follows. [I have two 3M M79s, full disclosure!)
Old Ampex 2" machines kick butt sonically, thick and full and punchy. Almost no one disagrees with this. You do NOT want to own one. Too much trouble. Need mods just to work properly.
3M M79 - musical, beautiful and clear. Not as "punchy" as Ampex but maybe more fidelity of sound (The M56 16 track is like an Ampex mixed with this, amazing.) Worrisome tech problems. Good news is - I paid $1000 each for the last two M79s I bought - lots of spare parts.
MCI - punchy, almost like a little brother to the Ampex, but not in the same league as the two above. MCI construction is detailed and thoughtful (VERY easy to service), crappy connectors all throughout.
Studer - there are so many versions. All sound good, built and designed very well, the oldest ones sound great, but punch badly and are tougher with parts and service. The newer ones are good but not quite as full and clear as the Ampex and 3M.
Otari - not that good-sounding, all the ones I've heard. Used to be my main machine, VERY good with tape. Easy enough to fix.
Stephens - rare, great sound, amazing design. Rough sailing if you want it fixed.
Scully - punchy like the old Ampex, but not as clean, tough on tape, some bits are very hard to service.
Soundcraft/Aces - run away!