If you know someone who is engaged, be sure to share this great resource with him/her!
Do you like their work? Do you love their posing and the emotions evoked when you see their portfolio? If you see mostly sun flare photos, note that that probably means it is an integral part of that photographer's style and so a lot of your photos may have sun flare. Do the subjects tend to be looking at the camera or more engaged in each other? Photography is an art form that is directly built into the photographer. If you prefer one over the other, this may play a part in who you choose!
Do you get along well? For a lot of your vendors, you will only see them when you book them or have appointments discussing your details or when they are dropping off things for your big day. Your wedding photographer is with you ALL DAY LONG. It's important that your personalities jive, and you enjoy being around them. How awkward would it be if you didn't actually like your wedding photographer but they were trying to elicit genuine love-y reactions from you?
Availability and Promptness
This may or may not be a a major factor for you but planning as a bride, it was for me! As a wedding vendor, I know brides have a million different plates they are trying to balance in order for their day to come together just right. So your wedding photographer should be prompt, not everyone can answer within a day or a few hours but I've heard horror stories about vendors who don't respond for weeks. Take note when you are communicating with your wedding photographer, how fast, and in what manner do they respond.
Check reviews of your photographer! While you should take everything with a grain of salt (both not so good and great glowing reviews), this will help access how others have responded and received services from this photographer. It takes a bit of effort to go and make a review so remember if these people really went out of their way to make these comments that means something!
See full wedding albums OR a full digital wedding gallery. Remember a photographer's website is the best of the best and their favorite work. Make sure you see a photographer's full and most recent wedding gallery. It would be great to see a wedding that is similar to your own. If you have an indoor wedding, make sure you see an indoor wedding and the same with an outdoor wedding. If you have an indoor wedding, make sure your photographer is good with creating their own light because most likely the reception venue won't be perfectly lit. If you are having an outdoor wedding, you want to make sure your photographer is comfortable with natural light and possible harsh sunlight if your venue doesn't have a ton of shade.
Some photographers only include digitals, some give the option for albums on top of digitals, and some ONLY do albums or prints. If you are looking at wanting to be able to share the images with your family and friends, an album only photographer may not be for you. A lot of people now use their images for invitations and thank you cards, so you want to be sure you can either order those items from your photographer (and that you like the products they provide) OR that you will receive the digitals so you can make those yourselves.
This may or may not be a big factor for you but professionalism can be quite the criteria and potentially affect a lot of areas of your wedding day. For example, if you happen to find a friend that has a photography business on the side great, BUT if this isn't this person's full time job, you may run into a few roadblocks or find that they don't have all the "kinks" worked out. Or maybe you happen to have a bruise or blemish that your hair and makeup artist was unable to hide from the camera. Does your photographer have the equipment or post processing program to be able to handle hiding such blemish? This may not deter you, but all that to say, be informed, know what you are getting into!
Let's be honest, though we all wish that money wasn't a factor it certainly can be. I think the best thing to remember here is to pick a photographer who meets all of the above criteria and then let it come down to budget. You definitely don't want to put price at the top and then end up landing on a photographer who mostly fits your style criteria but who's personality you don't jive with. Speaking from experience it's no fun to be that married lady on the plane to her honeymoon replaying the wedding day and those things you wished you could change. One of the number one regrets of brides is not investing in the vendors they REALLY wanted. Most photographers have payment plans! Just ask!