Our photographer was Ty and he did a great job for us. I know a few other brides have had him as well and I have heard nothing but good things about him. I know there are a few others, but I can't remember their names.
A couple of years ago, Disney's policy was to assign a photographer to you. You didn't get a choice. I think that has changed and you can request a photographer but I'm not sure if they guarantee you will have that person.
My suggestion (and this is regardless of using a Disney or outside photographer) is to have some idea of the type of photos you want. Look at lots of wedding pictures here and online and let your coordinator know what you looking for (specific poses you like, things you don't like, etc.). Also, don't be afraid to ask your photographer on the day of the wedding if there is something special you want. We wanted a particular picture and told Ty, he took that picture right away.