If you got money, get a MZ-S. It's probably the best AF film camera by Pentax (although some would prefer cameras w/ on-body Av adjustment).
If you want features, get a *ist or MZ-6/ZX-L, these cameras probably have the most features (other than the MZ-S) for the money.
If you want robust and fast fps, the Z1/Z1p is a good choice, especially its price is really low nowadays.
If you want an AF film camera w/ some classic look and feel, the MZ-5n/ZX-5n or MZ-3 is the one to go. These are probably the best combination of MF and AF cameras on the same bodies, that's why Pentax even made a MF camera out of the same body - the MZ-M/ZX-M.
I myself have had MZ-S, MZ-5n, MZ-3, MZ-6, Z1, and an earlier SFXn, the one I'm keeping is the MZ-3, for its AF capability and classic look