If you're really looking for unobtrusive, then it would be an XA. Although it has a rangefinder, it is hardly needed with the 35mm lens. The 35RC has both a shutter priority and a manual setting, and is proported to be the smallest full feature rangefinder of the chrome age (Cameraquest's opinion). Adapters for the mercury cell are readily available or use a zinc air hearing aid. The 35SP in a legend, with too many avantages to list here. See this great write-up about it.

http://www.ph.utexas.edu/~yue/misc/35SP.html

You might get it for $125 at that auction site.