DEFINITELY D90. although they're not on the same level as DSLR cameras. 550D is an entry-level DSLR while the D90 is semi-pro.. Why D90? it has more focus points (11), 4.5 fps (faster with continuous shots vs. 3.7 fps of 550D), you can use really high ISO and get minimal noise (plus naa cya noise-reduction daan) , and etc.. don't worry about 12MP from D90 kay MP (megapixels) is only important if you print your photos.. 12MP is really good na. it's semi-pro level but it's as easy to handle as entry-level cameras.. bias ko kay D90 user man sd ko hehe but trust me, di jud ka magmahay bro.