I am more familiar with Nikon
My first serious camera ended up being a Nikon D90, I would say more out of coincidence than conscious choice. Unless you are really annoyed by the company, there is a good chance that you will stay with the initial manufacturer you have chosen. At least that is what happened with me. Again coincidentally, at my work place they also had Nikon equipment.
After a while, you get used to settings, user interface, location of buttons, and you get much more familiar with available equipment. Once you make the step and start acquiring more lenses or even cameras, moving to a new system becomes more difficult. Especially since most of the manufacturers all make excellent equipment, so such moves between manufacturers is only rarely motivated by technical arguments.
Nikon Lenses on this wiki
Nikon Cameras on this wiki
These pages are for Amateur Photographers and not really for seasoned photographers and professionals. I have no affiliation or commercial interest with any brand/make. I write from my own experience. I ended up using mainly Nikon, so I am more familiar with this brand than others. See price for notes on pricing as well as photography related links.