So far as I know, SONY is a better option for sports, since it has a higher shutter speed. I'd recommend to read through Ken Rockwell's reviews on these cameras, will give you a better idea of what option to stick with.
Sony a6000 with 50mm is good for portraits. But, when it comes to sport photography, you will need a telephoto focal range. Sony doesn't have much collection of budget lenses in the telephoto range. In that situation Nikon or Canon one would be a better choice.
Had time to tinker with the a6000, and concur that portraits come out nice. Sony's lenses are not the cheapest, but you don't have to go with the brand all the time, there are other lenses that work well with the camera.