The Super Fujica-6 is pretty well made, film advance has been trouble free, it has a good viewfinder and very decent lens. They can be a bit hard to find outside of Japan though.

The best made and most rigid folder I have (& I have a few...) is the Certo Six. The f2.8 Tessar lens is unit focused, and is parallax corrected (watch the lens move as you focus). Its weak point is the rangefinder "mirrors" can degrade, but I replaced the one in mine from some beam splitter mirror I got from the Surplus Shed. The only other point against it is that the focus lever will foul the tripod plate - without a modified plate, you're stuck on infinity or 1.5m...

The one I like using the most though is the Iskra.