If your going to bother replacing the speakers you might as well get a component set that is designed to go together instead of trying to replace on set at a time. Are you saying that you want to use the stock speakers in addition to another aftermarket set? I would just replace all the stock speakers.

As far as picking speakers i would go to as many shops and listen to as many speakers as you can. Speakers are a personal preforance and some will like what others don't.