If you are going to get a chance to handle a variety of cameras, I bet the answer will come pretty quickly. Some models may not be available, some may have obvious problems. Not to be silly, but in a way buying a used camera in person can be like getting a kitten. One just finally jumps up and leaps into your arms and says, 'Take me home!'
I would suggest that a Yashica-Mat is about as low as you want to go on the quality of build scale. So handle one or two and get a feel for what a good build is like. Focus should be smooth, focusing screen should have some pop to it, the shutter release should have a smooth feel, and winding should feel solid (Yashicas can be noisy, but it shouldn't feel as if you are grinding something).
Check lenses- open the aperture, set to B, open the back and fire and hold open while looking through.
It'd be good to carry a test roll of film, and a spare spool. Load the film and run it through its paces. When you get to frame 12, open the back and look at the paper- '12' should be at about the center of the film gate. This should give you some idea if the counter mechanism is working.
Any of the cameras people have recommended will do you well, as long as you get one that works and has a clean lens and is aligned ok. Oh, be prepared to replace the light seals on the back.
Happy hunting!