I picked up a Leitz Pradovit Color 250 off of eBay a couple years ago. It's a very nice projector, though definitely old school. I don't have a problem with slides popping in and out of focus in this projector, as the Leitz engineers directed a stream of air warmed by the bulb across the next slide to be projected.
I don't have the Colorplan lens; I think mine is the Hector lens (I'd have to go look) but it's adequately sharp for what I do. Slide advance is smooth, and jams are rare and easily corrected, even with older slides in cardboard mounts that aren't so perfectly straight any more.