The reason i chose Nikon is because of lens backward compatibility, the AF-D lens can still be mounted and meter on my film workhorses FE and FM2, and be used on my d90. However the AF-D lens can't auto focus on d40, d60, d3000, d5000 due to lack of in built motor in the body itself. But these reasons doesn't mean that i can't use them, as manual focus is still an option. The newer AF-S G is an issue though, does not allow me to set desired aperture on my film bodies.
Not advertising for Nikon, but the primary reason why i chose them. Perhaps when u want to experiment with film in the future but do not want to spend another big sum on a set-up, u might want to to consider this factor.
Looks like you have decided on a Canon 550D, anyway irregardless of what you choose ultimately, most important thing is to go out, shoot and start having fun