Convert multiple formats to one format for editing?

Hi,

Trying to produce a video using clips from a variety of sources in Prem Pro. Am I better off converting all these clips to one standard format first? If so, which one? Clips are in every format you can imagine. I intend to imbed Jpeg stills, do some slow motion and add MP3 or WAVE audio tracks.

Output will just be a file, not a DVD.

Thanks,

swjtx99