The C100 is 4:2:2 8 bit, although the Canon log gamma handles this well with the Ninja 2 so it's nothing nearly as bad as AVCHD, let alone dSLR footage. That said, I consider the Ninja 2 to be a really inferior piece of gear, although it gets the job done and obviously provides files that are as good as any other recorder... but the screen is horrible and the pulldown detection poor. Unreliable, too. If you get the black magic camera (which I don't really recommend, but the quality should be the best available for the money) this is a non-issue as it records in better codecs and has excellent DR. I have heard it is a popular B cam for the Alexa from steadicam operators, and that is high praise.
4k is nothing to worry about until a client demands it... I have yet to see evidence that it matters since I've yet to see a 4k display. It's THAT far from being adopted by most consumers. Even most DCPs are 2k projected on 4k projectors. Furthermore, the Epic isn't a lot sharper than the C100/C300/Alexa, as they all derive 1080p from a generous oversample. Don't believe the hype. The Epic handles tungsten light and low light poorly; it's better for very high end stuff than lower end stuff, especially since the footage takes a lot of grading to shine. The Dragon looks cool, though. That said the Epic is pretty good for what it is, just not substantively better than lower resolution cameras overall... just a little less blocky when you punch in or crop.