I go for a lot of factors:
- versatile: can go with a lot of different oufits from work to casual, unless I'm looking for an evening bag
- color: I stay mostly with black and chocolate browns, for the above reason but there's always room for an exception
- great quality with stitching, heft, zipper or snap closures, material, lining, etc.
- easy to get in and out of
- has a cell phone inside pocket
- looks good on me proportionately