Many things.Originally Posted by snaplover
For example, if you like to take photos with flash, go with Nikon. Nikon famous for its CLS (Creative Lightning System).
If you have plenty collection of lenses from many brands, you can use Canon. Canon mount with correct adaptor can use lenses from other than Canon (for some extent).
Read more to gain your knowledge before you decide a camp. Once you decide and build up your camp, it is costly to change camp .
I hope above help.