Yeah, the GH2 is pretty great for video if you couple it with the right lenses. It just has a particularly awkward interface and good lenses are expensive and proprietary. Plus it's tiny and skewy so it really needs camera support.
Your question is kind of like asking should I get a Lotus or a Land Rover? Both are nice cars, I guess, but they target different audiences…
I wouldn't start with the Black Magic Camera; it's expensive, has a weird sensor size, and all-but requires a knowledge of post to use effectively (at least based on how it is marketed--Resolve is included, and while Resolve isn't that difficult the theory behind using it well can take weeks to learn). It's untested and unknown and I bet it's of limited utility relative to other cameras in its price range. It almost certainly has the best image quality, though.
dSLRs are tricky because they provide a lot of the look of high end cameras without providing some of the really helpful stuff better cameras have--resolution, a lack of skew, highlight handling, methods for focusing, decent audio, etc. and all the stuff you need to make dSLR content look great (lights, lenses, art design, camera support) is the same thing you need with an Epic or Alexa. They're awesome cameras for music videos, short films, etc. but pretty bad for videography…well, depending on the venue. If you must have a "shallow focus" look that's about all I can recommend dSLRs for (and then I would recommend the GH2 as another good option).
If you get a dSLR or Black Magic camera also buy an external audio recorder and prepare to sync audio in post. Which might be good practice for anything. I don't think dSLRs are good for improv or loosely blocked material because you need to hit focus marks and most ops aren't also genius ACs.
Channel 101 stuff is funny without production value. I find those videos hilarious and I'm bored to death by 99% of the stuff on reduser or dslr websites; it's all just camera tests with the occasional striking looking video. Most of the top youtube channels have pretty basic production value. Do you want to focus on writing and directing or being a DP (or very technical ad or music video director)? If you want to write and direct, I'd get the cheapest camcorder with manual controls and a good mic and some basic lights. dSLRs are deceptively expensive because of the cost of lenses and support gear, but at the low end they offer amazing price/performance for a "film look." They're best if you already know why you want one (down to which lenses and filters you'll buy, specifically), so if you're asking this question you should first ask: what do I want to focus on? Story or technique?
