No need to have two versions installed, just pick the one that's more convenient to you. Steam downloads and places the exact same files to your hard drive if you use Steam. The itch version is always the latest official release, but Steam also has a newer optional beta testing version of DRS if you're interested in trying out new features in advance (while potentially suffering more crashes because of the nature of the test version).
EDIT: Don't forget to check the Steam workshop for more content if you decide to use Steam instead