Hard to tell.
Including Protheans and Forerunners
and Mass Relays and Rings (LOL)
Edit: Precursors too...
Edit 2: ALL OF THE STUFFS IN THE UNIVERSES EVEN TREES
[Edited on 03.25.2012 2:43 PM PDT]
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Mass Effect= filled with spacefaring species at least the size of the UNSC with their own frigates/Dreadnaughts/Battleships, AND the Reapers AND the Protheans Halo Universe= UNSC and the Covenant, and Forerunners Mass Effect wins no contest.