Both series are awesome.
That said, Mass Effect actually evolved in all phases throughout its iterations whereas Elder Scrolls peaked with Morrowind in many aspects and then recovered (very,very nicely) with Skyrim.
If someone ever comes up with an RPG with the combat aesthetics of ME3 and the utterly expansive, life consuming, completionist devouring, mind blowingly orgasmic depth of Morrowind I believe I shall have a very antisocial decade or so.
"When you're running at me like that and I'm running at you...It's gonna be a nasty scene" BAMBAM!!