I've used the bmpcc, 5D2, 5D3, t2i, a7s and more high end camera's(sony FS,RED,...). First rule: if you want to make good looking images, lighting, rigging and sound is the most important part. Next is lenses and lastly the camera you shoot with. Invest accordingly.
Every single camera has it's flaws, even those lovely RED cam's. You need to look at what flaws are most workable with what you intend to shoot. If you are only going to be making films/music video's or similar things where you have the time for separate audio and decent lighting, offloading footage on set and when you can afford all the required accessories to make it work: BMPCC all the way.
If you're more in a run and gun type situation go with a gh4 or a used fs100.
If you need it cheap, buy a second hand canon(t2i, 5D2, t3i,...) and throw on magic lantern. Don't use RAW on it unless you can afford to lose some shots from time to time.
Watch reviews on all your candidates from good sources(Philip Bloom for example).
If you're ok with not having a tilty screen and not having full frame, a used 550D is great.
If you're thinking used 7D mk1 but want even cheaper, go with the 550D, those should be much cheaper, have the same sensor as a 7D whilst being much lighter and a bit smaller. Both it and the c100 are aps-c and you can use the same lenses as the c100. Throw on Magic Lantern for all the on screen tools and you're good to go.
If go low budget cam(this is also my suggestion) and have money to spare on lenses get some decent basic audio too, something like a rode videomic.