When considering a photographer, ask prospects to show you complete albums, not just portfolios of their best shots. Look for the obvious features that distinguish a good photo such as lighting and sharpness of focus, but make sure too that this person has captured the emotion and excitement of the moment. Ask about the photos themselves, are they printed on Professional Paper. This will make a difference to you as the years go by and your cherished photos are  fading away.
As a final point, be comfortable with the photographer as an individual. Is he/she likable and sensitive to your needs? Will he or she be the one who come to your home on your special day?