Slide scanners are going to do a better job scanning slides than a flatbed scanner with a slide adapter. Usually the dpi is much higher, but, more importantly, it actually designed to deal with slides. For example, flatbed scanners expect the media to be flat on the glass, but a slide will hold the film away from the glass by a millimeter or so. Higher-end slide scanners also have the ability to detect scratches and dust by also scanning non-visible wavelengths, which can be handy when retouching.

I don't know anything about specific models any more. This is all based on research I did a few years ago when I had a project very similar to yours, which, also similar to yours, I haven't gotten around to yet.