Both are awful by today's standards and incredibly by two year ago's. The 5D has three or so stops better low light, but both look fine at low ISOs. The sensor is obviously bigger. There's no aliasing or moire. Both are very soft and flat and difficult to post with and have mediocre DR.
Long story short, get an C100 (or better).
why not just load up ML RAW???
I recently made the jump to a c100& ninja2 and am loving it.
even beter iso performance than 7d, 5dm3, sharp, better ergonomics and controls.
would love to have a camera that can do both great stills and great video.
But todays dslr's are simply to crippled to do it.
even the c100 is crippled with a non broadcast codec but with a ninja you get to a broadcast level.
the 5dm3 can do the same via hdmi-mini-out but that conector is so flimsy its just not safe enough to rely on.
same thing with sound, client worries aside i never had troubles with using a external recorder and syncing in post via pluraleyes/dualeyes.
But i did have problems recording externaly and directly on the dslr via 3mm minijack (bad connection=no sound=nothing to sync with).
Now just plug it in the camera..why didn't someone think of this before
If the 7dmark2 gets closer to the Cine camera's than i'll get one as a second cam
magic lantern on the 5dm3 is greath but raw functionality is only usefull for short clips/shots not if you plan to shoot 1hour+ of footage on a day.
It would be great if some smart programmer could unlock the c100 and make it a even beter cam.