If the images are documentation of specific places or events and have certain evedentiary value, I would give a certain preference to RAW, DNG, or similar formats because of the extra layer of trustworthiness they provide (i.e. you cannot edit and re-save a RAW file as RAW, so you can trust that it hasn't been altered or re-touched). If the goal is to document process, version files are what you're interested in keeping. If the images are more along the lines of art photography or everyday-life documentation, final versions might be all you want to keep. Of course, available space and the content of the collection play a certain role here, as well.
As far as format choices go, there are lots of tools out there to move between image formats for preservation and access, provided the native format isn't already completely obsolete. No matter what the nature of the collection, you should (in my opinion) have a preservation TIFF or JPEG2000, JPEG being the runner-up (and a good choice for an access copy). Whenever possible, I'm a fan of retaining files in their original format as well. After that, more formats and more versions are documetary icing on the digital cake.