Canon and Nikon has been doing their fair share of the market for eons of years.
Sony is only good for doing AV systems. Stick to that
lol
Why I prefer Canon over Nikon ?
Just name a few reasons. The price is right for the camerabody in the market. The Canon lens selections is pretty wide as Kai said. The Nikon lens prices are way expensive compared to Canon which is cheaper but just as great products. for smaller amount of money.
Layout. (Example)
Nikon 1/3 Small selection but great stuff offered by Nikon.
Excellent
ED glas products, but quality=expensive . You got quality alright..
Canon 2/3 There are atleast a dozen more products offered by Canon used by prof- photographers out there.. compared to the small but good stuff offered by Nikon.
Also excellent
L glas products, but same equal quality=cheaper on the Canon side.
This is ony my POV, I bet the Nikonians will disagree/flame me for this. lol