help me choose a Camera.

[Anbesol]

May also be worth checking out the Olympus OM-D, with adapter, you could attach older manual focus lens. For low light, a fast fixed manual focus prime is a useful tool to have. Same with any micro four thirds and NEX system. The Fuji X-Pro 1 is a phenomenal piece of equipment, but pushes the budget a bit and has limited AF gear.

DSLR will have greater autofocus capabilities though, but only if you have a fast lens with it. The A77 kit has a fast 16-50 f/2.8 zoom lens for $2k, but should still be supplemented by a faster fixed lens.

The most important thing for you to do in order to accomplish your goal is to get a fast lens at the right focal angle for you. Aside from that, you could pick the "worst" camera now and still be better with a fast lens. What focal angle depends on what you want to shoot, what do you intend on shooting as fast action/low light?