For me, it boiled down to technology, price and weight. At the point of time I had to make the crucial decision between Canon EOS 630 or Nikon F801, both were on par in terms of features, tech specs and price.
But I decided on Canon based on the following factors, which I believe still stands today.
* Innovative - Ultrasonic motors, Full electronic contacts,
* Intuitive - revolutionary and IMO better User-Interface.
* Cheaper - at least for comparable lenses and flashlights
* Lighter
Nikon was known to be very reliable, even in the extremes of condition, and I didn't have a clue if the EOS could last. But now, after 14 years of owning the 630, I've only had to change the shutter once due to grease, everything else is working as it should be.