Obviously, appearance draws me in. Then, quality and practicality. I have to try a bag on before I buy and figure out if it fits my size and my style. Price is important, but I usually have a figure in mind and go somewhere that carries that price range anyway.
Size and colour first. If i'm at a particular phase where I'm looking for Big brown bags, then I look only at big brown bags and try to spot one i like. Then after awhile, i move on to say, small red bags..
First I go for the leather and the inside material. I love good quality leather. I love comfortable bags-ie: if it rests on the shoulder well and is in proportion with my body, etc. Detailing, like stitching and hardware come next. Then the overall price-is it worth it or not?...
leather, I love distressed, lived in leather or soft and supple leather. The bag has to be roomy. It has to be large enough to hold regular everyday items. Also small details, like whipstitching, padlocks, buckles, metal that doesn't tarnish. Lastly, style-I love classic, timeless bags.