"Don't join the loudness race which has no winners!" (Bob Katz) In general, don't overcompress! Rock/Pop/Techno/Hip-Hop/etc. should be mastered at -14 dBFS RMS. Classic/Jazz/Spoken text/etc. should be mastered at -20 dBFS RMS. Of course, those are rough guidlines, and your material may require different leveling.