I want to shoot:
For Concerts and low light events, FF pulls way ahead.
For Portraits, FF is definitely better.
For Street photography, a smaller unobtrusive camera is better, I would use whatever DSLR you choose, but if I bought a camera just for street photography, it might not be a DSLR.
Personally, I'd recommend a 6D for its low light performance. The other issue, as a previous poster mentioned, is lenses. When you are on a budget, you can find excellent Canon lenses on the used market easier than the other brands.
Does your $1200 budget include lenses? If so, you do indeed need to backup and rethink. Plan on spending 2X the price of a body on lenses to begin with, and more later on.
So, with a total $1200 budget, I'd dig up a old Canon film SLR, and take advantage of the Canon loyalty program. Trade it in for a REFURBISHED camera - lens combination and get 20% off. The refurbs have a 1 year warranty, and are typically perfect. A few high end bodies are held back, but you can get a nice 60D for under $500, which will leave you room for some good lenses. You will want f/2.8 or fast primes for Concerts.
+1 The 6D + 85 1.8, 135 2.0 or 200 2.8 are probably the best mid-range price options for concerts and portraits, but even the lowest price options (refurb 6D using Canon's loyalty program + used 85 1.8 ) will cost you between $1,600 and $1,800 which looks to exceed your budget and you would be pretty limited with just one prime. Adding the least expensive, flexible Canon zoom, the 24-105L would add another $650. Full frame is terrific, but still not real inexpensive to get started...
Given your budget of $1,150, APS-C probably makes more sense. As Mt. Spokane pointed out, you need a decent camera body, but lenses should really be where the majority of your money goes. Bodies are a short term investment while quality lenses will last you for many years or even decades.
My recommendation assuming $1,150 is a hard budget, is to buy a used or reburb 60D or T4i(650D) for
around $350-450. Get a 85 1.8 for $350 new or maybe $280 used and a 18-55 kit lens, preferably an STM for some focal length flexibility. Assuming you stick with photography, you will eventually want to replace your camera and kit lens with something better, but this kit would give you a great start for concerts and portraits. For street shooting, both lenses are fairly small and compact with a Rebel or 60D, maybe not ideally small and inconspicuous, but not bad.
An inexpensive speedlite that you can use to bounce flash should be your next priority, as on-camera, direct flash makes some pretty poor pictures.
I'd suggest a used 430EXII (maybe $250) that you can use on-camera to bounce off walls and ceilings or (even better!) off-camera, triggered by your built-in camera flash using optical triggering. Using speedlites really opens up a new world of possibilities for portraits and many other types of photography. There are some good off camera flash tutorials online, but I'd really suggest getting a copy of Syl Arena's "Speedliters Handbook", well written and covers the topic extremely well. B&H sponsors some speedlite workshops by Syl that you can find on YouTube as well.
Regarding your decision between Canon and Nikon systems, both are obviously excellent or they would not be #1 and #2 in the world for DSLR sales. I looked at both systems and chose Canon for the following primary reasons:
- best full "system" of hardware including bodies, lenses and accessories (lenses especially excellent)
- best support/service in the industry
- long term commitment to lens mount systems
If you are like many of us, you will acquire a fair number of lenses and accessories over time that will tie you to one manufacturer, so I think its important to look at the long view and each manufacturers history. You don't want to invest thousands of dollars on lenses and accessories only to have the manufacturer change their new cameras to a different/new lens mount system a few years later (Sony has bad track record in this regard), leaving you with lenses that can only be used with outdated bodies or forced to use an adapter. I plan to keep my best Canon lenses many, many years and will probably go through several generations of new camera bodies before they need to be replaced.