In a nutshell, PhotoPost currently has more features, can be standalone or intergrated with forum software, and is more expensive. vBGallery, formerly vBaGallery, also currently has more features, requires vBulletin to run, and is more expensive. PhotoPlog, with more features in the works, requires vBulletin to run, and is the least expensive. To get a sense of coding style, take a peek at PhotoPlog Lite
here. There is also a list of gallery scripts
here that may be of interest. Regarding support and development, both PhotoPlog Lite and Pro are being supported on this site, and PhotoPlog Pro development continues, with the next major feature being custom fields.
Update: custom fields is complete.