I discovered an Agfa Clack in my parent's stuff, and immediately grabbed it. This is a MF snapshot camera, kinda like a Holga, but it has a really neat curved film surface. (I was going to say "film plane" but it's not planar, it's curved) The idea is that this feature overcomes the poor performance of the meniscus lens, so it shouldn't suffer from vignetting or corner softness.
But to my discredit, I've never found out. 🙁
My least-used cameras are an early Voigtlander Bessa (I got the Bessa RF, so no need for guesstimation focusing with the original Bessa), and a Canon EOS Rebel Ti that I keep around just in case my digital EOS camera takes a dump during a wedding. I dutifully load film each time, then unload it afterwards... I've never needed the backup, thank goodness.
Mark