Sorry for the late reply but I was very busy for the past 2 weeks. I hope its no too late. :) I really love my 550D and I don’t have anything bad to say about it. :)
From what I read, Nikon D3100 and Canon EOS 550D are on the same generation of entry level cameras. I have many friends who use Nikon but I prefer Canon. For canon cameras, you can buy any brand of lens. As for nikon, you can only use nikon products and accessories with it. Well, my friends prefer Nikon because of its wide array of creative settings when taking a photo. But I don’t like to use different settings anyway. I prefer editing raw images on my laptop after to achieve a desired effect. In that way, you can do a lot with a single image. :) Both cameras are good for entry level photographers. Both have HD video shooting capacity, which is important if your gonna take a lot of good videos. D3100 is cheaper. Of course, you always get what you pay for. :)
The best thing you can do is try it out for yourself. You can go to stores that sell them and try which one you prefer. Or… You can also read a lot of comparisons in the net like…
http://snapsort.com/compare/Canon_EOS_550D-vs-Nikon_D3100
http://www.pocket-lint.com/news/35054/nikon-d3100-vs-canon-550d
Hope that helps. :)
