Either camera is capable of excellent photos, and for a beginner there isn’t a wrong choice here.

The main tradeoff mentioned is this: the T2i is newer and offers higher resolution and stronger video specs, while the D90 is a more advanced body with better handling features like dual control dials, a larger viewfinder, and a faster continuous shooting/buffer. Several responders felt those control and usability advantages matter more to learning photography than extra megapixels.

The bigger long-term decision is the lens system. Buying a DSLR usually means buying into Canon or Nikon lenses and accessories, so consider which system has the lenses you’re likely to want later.

Also, if you expect to stay mostly in auto mode, think about whether you really need a DSLR at all; a high-end compact can also give very good results in a smaller package.

Bottom line: if you want to grow into photography, either is fine, with a slight edge to the D90 for handling. If possible, try both in person and choose the one that feels better in your hands.