The Sony/MCI and the Studers are all wonderful machines to be sure. But, for a machine to listen to Tape Project and other pre recorded tapes, the 5050 would be you best bet. Large studio machines are,.. large and very expensive to maintain. An APR 5000 with only 30 hours on it sounds innocent enough, but if it hasn't been run recently, it could easily cost thousands to get it running properly. The prices vary on condition and options. I've never seen a full refurbished one for sale but most seem to sell for under $2k. I'd think that a refurbished one would be closer to 3-5k.
If you have plenty of money and room, that's a different story. But, if you're like most of us, it's better to spend the extra dough on one of Doc's repo amps (if you look at the Tape Project home page under machines).
The Otari's are making some inroads around here lately. More folks are looking at them as a logical subject for modding and upgrading. They are plentiful (which makes finding one you can actually try out and see in person pretty likely) and have been real workhorses in radio and project studios.
What machine is best for you, depends a great deal on whether you enjoy doing any DIY work. If you don't, I think the choice is pretty simple. Have Doc set-up a machine with a repo amp, plug in your favorite tubes and cables and enjoy.