Last year I went through the process of choosing a new camera. This included months of browsing, research, analysis (I have a peculiar fondness for spreadsheets) and limited in-shop tests. In the end, I chose the Fujifilm X-E1 and I still love it although there are already a wide selection of newer cameras on the market.
So these are my thoughts on what are the best choices out there if I was looking for a new camera today. You'll notice that I won't talk a lot about image quality (or sensor size or megapixels). That's partly because almost any camera on the market today from the main manufacturers is capable of great image quality. But also because the photographer, and to a lesser extend the lens, will make a far greater difference to the quality of the image than the technical spec of the camera body.
What does make a difference is how the camera feels in the hand, and how it makes you feel using it, how comfortable are you using it and how quickly can you change settings when you need to without being distracted from your intended subject.
With that in mind, these are the cameras I'd be considering.
Fujifilm X-E1 (under £500)
There are plenty of excellent cameras at the lower end of the market, but also a few problems. The kit lenses that come bundled with the cameras may not be too good. The main difficulty though is if you want a viewfinder. Many of the cheaper camera rely solely on the rear screen, which can be very hard to see in bright light. Fortunately there are now a few older cameras that are heavily discounted from their original prices. The Sony NEX6 and Fujifilm X-E1 are both still great cameras, with good viewfinders.
Panasonic GX7 (Under £750)
Aside from the Canon and Nikon DSLR ranges, Micro Four-Thirds cameras (basically all Olympus and Panasonic interchangeable lens cameras) have the widest selection of lenses available. The lenses are also slightly smaller than most, due the the slightly smaller sensor size.
The GX7 is well-specced, a great size, good looking and very capable. Features like the built-in wifi and tilt-able viewfinder make it very flexible, and the price is reasonable. The smaller sensor size was one factor that put me off Olympus and Panasonic initially, but with ongoing positive reviews from professionals they should be on your shortlist.
I'm biased in that I love my X-E1, but Fuji have chosen a great direction with the X-series of cameras. The retro styling is nicely done, but it's the physical controls that, for me, set the Fuji range apart. Aperture controls on the lens, shutter speed and exposure compensation dials on the body. And now with the X-T1, ISO control on a dedicated dial too. To me, this is a much more intuitive and fast way to control the camera than using on-screen selections.
The X-T1 isn't cheap, but it is weather-sealed, has some clever focussing software that makes it significantly faster than the earlier Fuji cameras, and built in wifi (although that is fast becoming standard on all new cameras). If you can afford it, the best Fujifilm camera so far and, taking price and bulk into account, one of the best cameras on the market today.
Canon EOS-1D X
I don't normally recommend DSLR cameras. Why? They tend to be large and heavy, and technology has moved on. Digital viewfinders are already so good that the mirror mechanism in DSLRs is unnecessary.
There are many exceptional DSLR cameras though and they can still outperform the mirrorless options at the higher end of the market, particular in terms of focus speed and robust build. If you specialise in sports or wildlife photography, then the speed and range of lenses for Canon and Nikon still make them the right choice.
The 1DX hasn't been without issues. Early models were prone to fail in very cold conditions, although that has now been rectified. If I was going to be photographing fast-moving sports for a living, and if the asking price wasn't an issue, this is where I'd look.
Olympus - The OM-D range have been receiving rave reviews, and have the full range of Panasonic and Olympus lenses to choose from. When I tried them though, I just didn't like the handling. Small buttons and, to me, the thumb grip just felt insecure.
Sony A7 - Sony has opted for a larger 35mm (full-frame) sensor in the A7 and A7R. Reviews have been excellent, and if the sensor size is important to you then this is one of the few choices in a smaller body. Lens options are limited though, and still large in size, and the shutter noise isn't the quietest.
Panasonic GH4 - If you shoot more video than stills, the Panasonic can record 4k video and has many design features to suit the videographer, as well as still being an excellent stills camera.
Fujifilm X-E2 - The update to my current camera has wifi and faster focusing. The X-T1 steals the limelight but if you want a smaller body and don't need weather-sealing, the X-E2 is a great option.
Fixed Lens - Maybe even the mirrorless cameras I've mentioned are too large for you and you want something you can slip in a pocket. The Fujifilm X100S would be my choice, with it's fixed 23mm lens and virtually silent operation. At a lower price point, the Fujifilm X20 (X30 rumoured to be due soon) or Canon G1X would be a consideration.
Leica - If you have the money for both camera and lens, find one of the Leica stores and have a browse. Either just don't tell me, or let me borrow it, ok?