Whichever camera body you get, I would strongly recommend getting one prime lens with a low number of glass elements. Zeiss makes several 50mm lenses that fit that description and that fit or that can be adapted to most current bodies (Nikon, Canon, Fuji, whatever). Voigtlander also make a 58mm that is similarly designed. By low number of glass elements I mean no more than 9. The reason is that sharpness, like loudness in an audio system, is the least interesting and most easily achieved aspect of lens design. A well made prime lens with a low number of glass elements will give you 1) excellent color rendition; 2) beautiful depth rendition; 3) excellent microcontrast; and 4) beautiful out of focus rendering.
1. Color rendition: not accuracy of color (which is controllable with adjustments on the computer), but the ability to discriminate between similar hues--rendering 100 subtle shades of green in a leaf vs. a dozen.
2. Depth rendition: how the lens transitions from in focus to out of focus in the photograph. Even at the same focal length and f-stop, some lenses portray that transition more cleanly, so to speak, giving a sense of depth and dimension to the photograph. Even expensive "pro" zooms with 14 or 18 elements will give flat results. Side by side the difference is obvious.
3. Microcontrast: related to color rendition, but even in a black and white photograph this ability to discriminate fine detail makes the image rich and beautiful. Traditional sharpness is edge detail: is the border between the hair and the skin crisp. Microntrast doesn't require border crispness as much as being able to perceive very subtle details where other lenses may not reveal them (such as textures). Another way to say it would be the ability to preserve differences in luminance (compared to color rendition: the ability to preserve subtlety of hue).
4. Out of focus rendering: Bokeh in Japanese. You can certainly get a smooth and pleasing bokeh from from a lot of lenses on full frame cameras, but low-element primes with large apertures on full frame sensors are the best of the best.
It's always useful to think of the lens collection you want first, because your investment in lenses, which you can use for a lifetime, typically exceeds the cost of the body by 2-5 times.
If you want a small mirrorless camera, the Fuji XT-1 is fantastic. Color rendition is excellent from the primes and even the zooms, and the jpegs right from the camera look terrific. I don't agree with many things kenrockwell.com writes, but I think he gets it right regarding the Fuji lens quality. I have the 35/2, 56/1.2, and the 18-135 for convenience (I've been very very pleased with the results).
However, although I own the XT-1, it can't really provide the ability to throw the background out of focus that a full frame sensor provides. So I also have a Nikon full-frame (D810).
I have a Sony Alpha as well, but I rarely use it. The Zeiss 50mm for the alpha is an amazing lenses, but the camera and all of the variants in the alpha line is a mess designed by committee, not a tool for photography. The lenses are all huge, making the system no smaller to pack or lighter to shoot; the battery life is terrible (add batteries to the weight you carry); the menu and button layout is sadistic; and there's no depth to the selection of lenses or system components (compared to Nikon, for example).
I used to use Canon digital SLRs but I just tired of the mediocre lens quality, even in L lenses, and the exceedingly plastic feel of everything they make. I know, with very careful lens choice and technique you can take beautiful photographs with a Canon. I just got too tempted by the infinitely deeper Nikon system and the higher number of exceptional lenses they offer (new and old). I've been picking up older manual focus Nikkors from ebay that are better then most current production autofocus G lenses.
If you decide to get a Nikon body, the current 24-85 ED VR is a terrific grab and go lens on a full-frame body. Add a Voigtlander 58mm Nokton and you have an amazing indoor, portrait, low light option (also beautiful for landscapes and any other need):
https://shop.cameraquest.com/voigtlander-slr-lenses/voigtlander-58mm-sliin-58/1.4-nokton-nikon-mt/For a Nikon autofocus prime lens for children indoors, the new Tamron SP series 45mm (45mm F/1.8 Di VC model F013) is probably the closest you can get to a Zeiss with autofocus on a Nikon.
For the Fuji, the less expensive XT10 has the same sensor and cpu as the XT-1 so is the best for the cost in their camera range.
Well, that's a lot of opinion and I'm not sure if it's helpful. Happy shooting!
