I could be wrong, but I think the reason they forked it is because TFS tries to stay true to the actual tibia version they are developing for, and the OTX guys wanted to use that as a base, but add support for other protocols, and also add other features not present in the tfs distro.
Having said that, if you're a programmer, OTX would probably save some work on adding additional features. If you are not a programmer, or not willing to hire one, you're better off using TFS.
I've experimented with both, and I have ran into alot of issues with OTX that are over my head to fix, as well as alot of small frustrating issues that cause me problems.
At this point, I haven't had any issues at all with the main TFS project.
But, take what I say with a grain of salt. Im nowhere near a good programmer, and not all that too intelligent.