All of the gaming tools by the RPTools Team follow a consistent versioning scheme. There is always a stable (also known as release) version that can be used by those gaming groups that have concerns as to the stability of the development versions, and do not want the latest and greatest features badly enough to justify the risk of complications. That said, it is frequently the case that a late development build is effectively as stable as a release version (this is currently the case with most of the recent MapTool 1.3 development builds). It is a good idea to ask around on the forum to determine which is the best build for you.
Development versions are where all of the glitz and new features are added. Because of the constant additions that occur in this version of the code, external file formats are likely to change, functionality may be introduced in one build only to be removed in the next build, and there can be usability issues as well. Anything major is normally corrected in a very short time (a few days is typical) but this can lead to head-scratching and a loss of sleep for those who like to live on the edge.
My general recommendation (I’m Azhrei over at the forum) is to use a development version that the rest of the community considers solid. To determine that would require reading the forums, primarily the MapTool forum. We expect version 1.3b91 to be the last build of the 1.3 version at this point, while we transition to working on 1.4.
My goal with the above is to give you an idea of where you might want to start. I often use a stable build of the development versions of the tools for my gaming nights, and then play with the bleeding edge builds at other times. I don’t want to risk a show-stopper in the middle of a game, but I don’t want to be too far behind the curve either!