There are many factors to consider when choosing a photographer, whether it be for a wedding, a family portrait, or a bar Mitzvah.
Probably the most important reason is the style of the individual photographer appeals to you in some way. You may just have a feeling that you like the style, the vision that this photographer has. This can translate into a video production as well.
The next consideration should be the photographers product line. Do they have the type of products that you can not get anywhere else or are these things you could possibly produce on your own given the time and resources. For example in wedding photography there are albums that are only available to professional photographers. These are leather bound designed for wedding or Bar Mitzvah photography. The pictures can either be mounted to the page that has a liner to give the picture a border or the album can be matted which means the picture sits in a matt on the page. Of coarse you would have color choices for all of this. But as you probably realize that to try to attempt something like this just is not going to be possible on your own.
Another consideration is the photographers skill in handling all the people he will be required to direct in order to get the pictures you want at your wedding or Bar Mitzvah and even for a portrait you must be able to relax and enjoy the experience. The key to wedding photography is to have your subject relax, posed but relaxed in order to capture their true personality. A good photographer will help you relax by keeping the mood light and fun, reminding you to take a deep breath and relax, to smile and enjoy the experience.
Wedding photography can be very stressful, everyone is under pressure to go here and go there, many people are putting demands on your time,. That is why the day seems to go so fast. That is why you need someone who can quickly and efficiently organize groups, take the picture in a light and easy manner so that enjoying the experience is more possible.
Whether you are planning a large event or a small gathering hiring the right professional is critical. Lastly consider the cost, that is really the final piece of the puzzle, you should select someone who you feel comfortable with, who can offer a photographic product line that is truly professional in quality and scope, and that persons skill in handling large and small groups of people efficiently and friendly as possible.
I hope this gives you some good insights into making an intelligent decision about hiring a wedding photographer, Bar Mitzvah photographer, a portrait or corporate photographer.