If you plan on buying a kit, and living with it, and not getting any other lenses then you will probably find that the image quality from the above are all about the same. The Sony is the smallest and lightest so will be easiest on the shoulder when travelling. The moment the light is low, you'll appreciate the nikon/canon as their low light performance is better.
So basically if you stick with the kit lens, the choice is probably viewfinder, ergonomics, weight, size. The sony is the light and small winner, but personally I find the viewfinder too small to be useful for compostion, and prefer the nikon/canon finder.
If you are planning on getting additional lenses for these cameras then you need to look at the lens ranges that are available and try and make a decision based on what you will want to do. In this range the nikon and canon clearly win as long established ranges so there is much choice of quality primes for these models. As a general rule Nikon make better wide angle, whilst canon make better telephoto lenses. A generalisation, but probably accepted by most. So if you are interested in landscapes, go Nikon, or if you are a closet birder, go Canon.
Of course the quality lenses will cost more than the £400 kit, so maybe it is not worth considering these, but you'd be surprised how good the images are from the cheap cameras with decent lenses attached.
Cesare