If you need autofocus, you'd be looking at Canon EOS, Minolta Maxxum, Nikon, and Pentax. (There are others, but they're usually outside of my price range.)

• I'd probably go with a Canon Rebel, despite the annoying CR123A batteries, because every EOS camera I've encountered so far has been functional. People get rid of working cameras because they can't be tested without expensive batteries.

  If you're patient, you can get them with kit lens for cheap at estate sales, thrift stores, etc. (< $20) Carry a pair of CR123A batteries with you to test. If the rubberized grips have degraded into a sticky mess, negotiate the price down even further. They clean up fine with nail-polish remover.

• I haven't tried any Pentax or Nikon cameras with AF because they usually don't have lenses I'm interested in. Also, people tend to ask too much for newer bodies, even when the attached lenses are junk.

If you're willing to focus manually, options include Canon, Minolta, Nikon, Olympus, and Pentax. It's reasonably easy to focus with split prism, even with mild uncorrected astigmatism.

• Canon FD, Minolta MD, and Pentax SMC lenses are all very good. Consider finding a set of lenses you'd like to use first, then pick a body to match. I like the Minolta Rokkor lenses slightly better than the Canon FD equivalents.

• If you want to use third-party lenses, it doesn't matter which camera you pick because lenses were usually made to fit all commonly used mounts.

• I haven't used any Olympus OM bodies, but I don't like the lenses as much as the equivalent Canon FD and Minolta MD lenses.

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Here's a list of camera bodies I've encountered while searching for old lenses. It is not exhaustive. The order is based on the battery type that's required. Cameras in bold are more likely to be functional, based on my personal experience. (I have a stack of broken cameras and a stack of working cameras that I haven't decided what to do with yet.)

• Canon T50/T70/T90 – Use AA batteries. T50 is full-auto only. T70 doesn't have aperture priority. T90 tend to be heavily used, so may not have much life left in them. Canon FD lenses are very good.

• Minolta Maxxum – Use AAA batteries. Lenses are compatible with Sony A-mount. However, majority of bodies that I've encountered are not fully functional. Minolta AF lenses are very good.

• Minolta XG Series (also XD, et al) – Use CR1/3 Lithium cells (equivalent to 2x LR44/SR44/357).  Cannot operate without power. Minolta Rokkor lenses are very good.

• Nikon FG (et al) – Use CR1/3 Lithium cells. Can function without batteries in when shutter is set to "M90" (1/90s). Old Nikkor lenses are an acquired taste (mild halos and veiling glare). Haven't encountered enough Nikon bodies to have a good sense of whether or not they're likely to be functional.

• Pentax (various models with K mount) – Use CR1/3 Lithium cells. Cannot operate without power. Most of the bodies I've encountered have some film advance/shutter issue. Pentax SMC lenses are very good.

• Canon EOS (Rebel G et al) – Uses CR123A batteries (expensive). Uses modern EF lenses that may also work on modern digital bodies.

• Pentax (various models with M42 mount) – Weird mercury battery, but only needed for the light meter. Takumar SMC lenses are very good.