I feel that the 111S is the best by far of the Retinas. Often overlooked in favour of the 111C or other folding Retinas, so they can be had for a less inflated price, If you can do without the folding function, these are the way to go. They have proper interchangeable lenses, the same ones as the later Retina Reflexes, and are just very pretty cameras. I have a couple of bodies, and a few lenses for them. The 50's include the Xenar, 1.9 Xenon and the Rodenstock Ysarex. Can't really pick between the two 50mm 2.8's, but the Xenon is a great lens, just a bit big on these cameras. I also have a 28, 35, 90, 135 and 200mm lenses, which are also adapted to fit on my Bessamatics.
As Mike says, the only real problem is sticky shutters (same as any leaf shutter) especially on the low speeds. THe 111s is not plagued by unreliability like the Reflex cameras, so should be very useable. One thing of note though, like all the later Retinas, the shutter locks when the counter reaches 0, not a fault, just Kodak trying to stop people getting that extra couple of shots out of the Kodachrome!