I used a Pentax KX (still my go-to film camera) but the 35mm SLR market was very competitive. The, "Big Five," (Canon, Olympus, Nikon, Minolta and Pentax) accounted for around 80% of worldwide SLR sales, while a number of smaller manufacturers (Cosina, Chinon, Ricoh) used the Pentax lens mount. As always, the cheap end of the market was the 42mm screw Zenit and Praktica models, while people with money bought Contax (shared a lens-mount with Yashica) or Leica (who made SLRs as well as rangefinders).
The advent of Autofocus (Minolta 7000) sharply curtailed the market as not only the smaller manufacturers, but even the luxury end of the market failed to compete. Canon got off to a flying start only by bringing out an entirely new lens mount (as had Minolta - now Sony) Nikon's heavier lenses made their autofocus system slow, and what happened to Pentax and Olympus' attempts can only be described as disastrous (Pentax' second generation of AF SLRs were much improved, and their DSLRs are superb, but they still haven't recovered from the blow to their reputation over AF).
Cameras to avoid from this period are 35mm Mamiya (rare lens mount which never quite worked) or Fujica (predecessor of Fujifilm, rare lens mount killed by the advent of AF).
If you can find either, the Chinon CE-4s and CE-5 are aperture priority/manual SLRs taking Pentax lenses, and are probably among the most under-rated SLRs ever made, otherwise, stick to the, "Big Five," Canon and Minolta MF lenses are fairly cheap and plentiful, as are lenses in OM or Nikon AI. While Pentax K was once the commonest lens mount in the world, old Pentax lenses still fit new Pentax cameras, so their prices are a little higher.