The MZ-S is without a doubt the best Pentax film SLR as far as feature sets go and ergonomics.
The PZ-1p is a great body at a low price, but clunky for my hands at least.
The LX is a hard and tough body with interchangeable finders and the ability to outlive any situation.
And the MX, for its great build and small size, it can do anything you need it to do, and still fit in your pocket with a pair of primes in the other.
Of course, the MZ-S is the best of the best, as far as use every day and working with, and to see one with the 31mm Limited mounted, its just beautiful.