I've used Unity and Unreal Editor and I like them, they are great tools. I just feel that they are unnecessary for the scope of Daggerfall.
More projects (not forks) mean more ways to skin a cat... just pick the one you want to help develop further. I just happen to prefer OpenDF because it is closer to how I like to develop, which happens to be C++ as opposed to "Daggerfall Tools for Unity" which uses C#. I don't care for C# (mono) and I hope it dies in a fire, but that is just my opinion.
From an end-user perspective, use whatever works for you!
Side note:
http://www.curly-brace.com/favorite.html
C# is very nice for quickly building GUI applications. Especially programmers used to MFC can't seem to praise C# loudly enough. But then again, if you are used to rusty pins being driven under your fingernails daily, the prospect of being kicked in the groin at unpredicable times but only once a week must sound really attractive.
