Nikon.
I have been through the same exercise as you have and I have found Nikon to be a much better spec'd camera and the kit lenses feel like they are much higher quality to me than the same Canon Lenses.
I have noticed (looking at the classifieds) that Canon are more popular so there are a lot more used cameras and lenses available. The cost of most lenses (new) in our country are the same for Canon or Nikon mount, so nothing to go by there.
All in all, I am more impressed with Nikon than Canon.
As someone said to me on a similar thread I started, you are buying into a system, once you make the choice and buy additional lenses, you are pretty much stuck with it. Make the right choice.
Personally, I think the Canon 1100D is a pretty low spec cheap entry level camera. The 550D would give you a better spec'dcamera but none of those compare to the Nikon D5100. This camera (no experience with it yet) has really impressed me from a specs perspective.
Just one thing, if you're buying a DSLR, no matter what they say about video, it's a "Stills" camera. Although the D5100 can take videos, it's not the reason I am buying one. (Next week)
I like the low noise at high ISO thing about it. Which means I can most likely get better shots in low light than with a 550D. Both using the stock lenses.