Yeah, Mars definitely had the greatest music in the entire trilogy.
Mass Effect 1 had some excellent tunes: Vigil, Sovereign's Theme, Uncharted Worlds, the Ilos battle theme, and the epic orchestra/synth stuff during the game's finale.
Mass Effect 2 has some really memorable stuff for me too, though. Suicide Mission, obviously, but the remixed Uncharted Worlds is great too. Reflections is great. Jacob's theme has some great parts, Tali's theme is excellent. The Collector Base music is intense.
Next to Mars, there's some other good shit in Mass Effect 3. An End, Once and For All obviously. Controversial though the scene may be, 'Wake Up' is still an incredibly haunting piece of music.