Saying one language is BETTER than another is totally subjective. You have to decide what your programming style is. DarkBASIC is designed to make Direct X programming easy - so there are a series of shortcut commands to manipulate cameras, lights, primatives, user defined objects etc... all available in a "traditional" style BASIC programming language. DarkBASIC is designed with the intention of a user being able to create a 3d game fairly easily.
I think RealBASIC follows VB in that it is a more object and class based type programming BASIC. I don't know if it has the same type of Direct X shortcut commands. I think primatives and such have to built from the vertex up - but I don't have a ton of experience with realbasic so you'll want to find that out.
What I like about darkbasic, is that I can set up a scene in sort of a draft mode, with a floor, and cubes and spheres as my test objects in about 2 minutes. I can then try different things in terms of moving them around, or testing collision, or whatever, to find a viable method for whatever my programming goal is (in terms of a 3d game or something). The commands included make this pretty easy. Then later, I can load models and textures and replace my test envirnoment with a real environment... I don't have to use external models, I can use primatives (cubes, spheres, cones...) and complete the whole scene in DarkBASIC. How complicated things get depends on the programmer and their imagination. If one has to go beyond the limits of DarkBASIC, then dlls cann be called for extra functionality.
Enjoy your day.