I went with Canon for one reason, Magic Lantern. Magic Lantern was the only firmware hack to open up the abilities of an entry level DSLR to more pro level additions like: mic monitoring, zebras, and focus peaking. The cost for me was around $350 for the body and a lens, and adding in Magic Lantern was free. The next cost for me would be lenses. Where was I going to get them and for how much. New prime lenses are still quite expensive for me, and anything greater than the cost of my camera wasn’t really an option. I looked around and even the cheapest Canon primes are around $85-$150. I kept looking and I came across KEH.com. They have used camera gear of all types and ratings. From nearly junk to pristine, you just have to pick from a list of lens mounting types (Canon EF, Nikon F, MFT, etc.). When I was looking there were a great many of the Nikkor non-AiS lenses, which fit the newer Canon EF-S mount, only needing a thin, cheap, metal adapter. Unfortunately these older Nikkor lenses won’t fit onto the newer Nikon bodies because there is a slightly too long bayonet on the lens, and can damage the mirror in the camera.
The Black Magic Pocket Cinema Camera (BMPCC) is prohibitively expensive for me. The camera itself will go through batteries like no ones business, the on board mic is terrible (like Canon’s), and there wasn’t as big an after market for Micro Four-Thirds (MFT) mount lenses- meaning more expensive lenses. You can adapt MFT-mount to standard lenses, but again, the adapter is around $500. Dynamic range, color reproduction and all that is much greater on the Black Magic, but at conservatively $1,000 more expensive, it’s not ideal. Consider the cost of not only the camera body, but the necessary accessories as well.
Don’t think of what you need right now, think of where you’ll want to go in the future. At the time I was looking, RED, Black Magic and many other camcorder manufacturers used either PL or EF lens mounts on their high end camera bodies. Investing in lenses that are EF compatible was an investment in the future for me. At the time I purchased my T3i, Sony was just getting into the mirrorless game with its NEX line, and they weren’t very good at shooting video. Now, with much more selection and variety, I don’t know that I’d do anything differently because the T3i is still the cheapest and… well… I’m cheap, I don’t need 4k or RAW. For you, choose where you want to go, and whether the accessories that you get for one system will work for another. Other than that, sky’s the limit. Get whatever suits your needs. Good luck!