There are a lot of excellent mechanical shutter camera bodies out there. What to get really depends on whatoyu want as a kit and the budget. A newer reliable system can be based on the Yashica FX-3 series. The Yashica/Contax lenses come in 2 series, The Yashica ML series is bargain priced and very good to excellent. Most borrowed on the Zeiss lenses Yashica was using for the Contax line of cameras. If you want better then the Contax Zeiss lenses are put there.
Another bargain is the Asahi/Pentax line. The M42 lens screw mount lenses are still some of the ones to beat. I recently picked up a S1a and it is the tank that Nikon F would like to have been. You could hammer nails with it and never dent it. I can not wait to try it out, I'm actually excited about a camera in a couple of decades. The viewfinder is large and clear and focusing screen excellent. Admittedly, it is purely mechanical, not even a meter. The Spotmatic is M42 mount and has the meter but, unlike most classic cameras the metering circuit is not a problem because the mercury battery is no longer available.
I agree that the original Leica SLRs also make the grade. But, they are a might rare and they and the lenses are somewhat pricey. But if you appreciate fine wines, cars and food, one of these might be the answer.
Now, to fly in the face of sanity, pick up an Exacta and have it surviced. Back in their day, the were 1st rate though quirky control layout compared to later cameras. There were a huge number of lens makers making lenses for the camera so you can have your pick from cheap to mortgage a house and from okay to some of the best. Also, you can have 2 views, a prism like most SLRs and a waist level finder. The acc'y range for the cameras is huge. Maybe the only item lacking is a motor drive, I've never seen or heard of one. Years ago before settling on a Bronica system my largest brand and range in my collection was Exactas and some of the finer photos I ever produced were with them.