I don't choose the brand, I choose the camera.
My first P&S was a Chinon, because I wanted a simple, cheap camera. "Focus-free".
Then I got a Pentax zoom, because I needed a zoom.
Then I got my first SLR, which was a Minolta, because I asked the dealer for something "idiot-proof". A point and shoot SLR.
Then Nikon came out with the Coolpix, so I got the 700 and later the 990.
Then Canon produced the D30, and the rest is history. But yes, I'm now locked into a Canon system, because my lenses are all EF mount lenses (not neccessarily Canon lenses).
I now understand that Nikon has more than one series of lenses, which are not all compatible with different Nikon camera bodies. That's sad. I'm glad Canon produced the D30, and not Nikon.