This is luckily a rather uncommon disease, but you can easily be infected by it. NAS simply stands for
Nikon
Acquisition
Syndrome. Being a freelance photographer I had made up my mind already 20 years and the decision has been for Nikon.
Why? I honestly can't say. I loved the F3 and its fast motor drive, since it was suitable for my sports photography at that time. Could it have been any other manufacturer? Maybe, but I still have been very happy with my Nikon equipment and have never regretted this decision.
If you are already infected by NAS or you are on the way to it, then this is place to be :-)