if you are interested in shooting video, the 550D is great. But, for photos, i like the 3100 a little better. Even though it is lower megapixels, It takes as good or better images than the 550D. Also, with the 550D packing that many megapixels on that sensor can lead to more noise at higher ISO. The 3100 is a much better lowlight camera because of this. But, the 3100 lacks an internal focus motor so older lenses wont autofocus with it. I also like the 3100's handling better, but that is a personal preference, so try to hold them both at the store. You can't go wrong with either, and its really a personal preference, so go to store and hold them both and go through the menus and see what you like better.