I might be suspected of bias, but the Daleks are the superior life form in the universe.
Well, if we're going by bias I would choose Precursors, even though we don't know anything about them. Heh. :P
But, seeing as how powerful the Forerunners were, it may be safe to say the Precursors are very much god-like. The Forerunners themselves had an empire that spanned millions of planets, built near solar system sized Dyson spheres, could traverse Slipspace accurately and even traveled to other dimensions (and to some degree, time), were able to digitize organic life in large quantities (the Composer), move planetary objects through slipspace and had intergalactic travel, created their own galaxy spanning "VR" (the Domain), built weapons that could destroy organic life on a galactic scale, etc. These guys were serious stuff! Now imagine the one's who came before them who also created them (and humans) and created the one threat that can devour entire galaxies and that's even ridiculously more powerful!