what you want to use it for
any other features you want
with a 2ms response time you're talking a TN panel monitor. its a cheaper option but image quality and viewing angles leave much to be desired.
1920x1080 (1080p) is pretty standard across the board.
led backlighting really doesnt give you all that much. current models are all edgelit which means contrast isnt any better. on cheap panels you run the risk of having a blue-tint to your screen (which i think you can adjust out somewhat).
panels 22-24" in size are fairly mainstream right now. you shouldnt have a problem finding many different models to choose from.