Install the Developer's Cut. It is the most recent version (though I don't think there were any changes to the game itself from DKS), and in the unlikely event there is another patch for the game, that is the version that would be updated. It also has an added, optional, Developer Mode cheat window.
Are saves compatible between all the versions? I have ED on disk, DKS on steam, and can download D2Dev. I've been playing Steam DKS on this character. The DRM removal tool, is it good for Steam?
Saves are not compatible between the original release of D2:ED and DKS / D2:DC (there were too many changes made when D2:ED was remastered). A DKS save should be fine in D2:DC, though at least if DKS is not patched (not an issue for the Steam version) it would have a problem with D2:DC saves (though if you have D2:DC there isn't much point to switching to DKS).
The DRM was removed already from the Steam version of DKS, and there was never any DRM in D2:DC.