I think asking "which old camera should I buy?" is a bit like asking "which old car should I buy?"

I would derive no joy from a 1960's cadillac, even though its an old car - while many would have no fun with the cars I would pick.

Same goes for cameras.

Good thing is - many absolutely amazing cameras are dirt cheap, and you have just about all of them accounted for in pages prior. Pick one. You can buy and sell them with no loss and sometimes a gain, as they seem to have hit the bottom of their depreciation curve. Buy one, see if you like it - if not, sell it and get your money back (if you bought wisely - not even exceptionally, just smartly).

One suggestion I would add, is a camera that is a bit of a hidden gem of the Canon FD line - the EF. NOT the EF-M. This is an ancient, all metal, old-school SLR that has just about every feature you can want in a manual camera - although it has some drawbacks (no motor drive, no replaceable focusing screens to name a couple - perhaps the only major ones).
It does have mirror lock up, is built like a TANK (warning - and wieghs as much!), has a mechanical shutter for all but the slowest (upwards of 1/2 second) shutter speeds, has a vertical travel Copal shutter and synchs with flash up to 125th of a second - pretty good for an SLR of that vintage. Also, it may be the only one that has a verified voltage comensation so that you can use modern batteries.

Big selling point - the meter scale in the viewfinder adjusts as you switch lenses - so with the f1.4 it started there, with the f4 it starts at f4. WOW.
OK - I am kidding, but it is a cute little gimmick ona 30+ year old camera

I enjoyed mine very much, until it was stolen out of my car this weekend

One more thing - I have an AE1, and I have a friend who bought one - they are both a huge pain with unpredictable electronic gremlins - I know they are wonderful when they work (mine is) and perhaps my experience is isolated and not typical - but the electronic shutter/meter gremlins relegated mine to paper weight status (even after getting many knowledgeable people's advice on how to get around them). And no, it was not the squeek. That much said - they are SO cheap... you can just keep buying them until you get a good one and whenever they give you trouble - but who wants to do that?

Peter.