I’m not a current user of either program, so I can’t directly answer this, but I can make a few comments and throw SketchUp into the mix.
Over the course of several years sitting on Masters of Architecture thesis juries, I often asked what software the students used. Several years ago, I would say it was quite consistent that the more creative designs were done in SketchUp (I could usually tell SU output before even asking), while the work done by by students in REVIT were, well, rather uninspired designs. In more recent years, I would say the use of REVIT among them has grown, and SU shrunk a little, and I’ve seen better design work done in REVIT, so I can’t say it’s such a striking contrast anymore.
General impressions: REVIT is the preference of large firms doing big projects, while ArchiCAD appeals to small to medium sized firms. REVIT is most credited for helping to work out construction details with features like clash detection between structural and mechanical elements. That’s not saying much about powers of design creativity. Sorry to say, but students learn REVIT primarily for the prospect of getting hired out of school, despite the fact that SketchUp’s advertising campaign is currently trying to make that claim. I think it would be better to pitch SketchUp as the choice for the star designer; the student who stands out as the best designer in the class, and wants software with the greatest flexibility and design freedom that will carry through a career, not just a job.
My first foray into BIM was with Architrion in the late 1980’s when I was trained to be a trainer, but by 1990~91 I gave up on it as not ready for real world projects. ArchiCAD appeared on the scene right on the heels of Architrion, but it has survived to today. In 2003, I picked up ArchiCAD and SketchUp and was experimenting with both, and, after a few years, dropped ArchiCAD altogether in favor SketchUp. Once and a while, I’ve gone to presentations on ArchiCAD updates, and I have to say it has improved.
The main thing is this: BIM software is some software engineer’s interpretation of how an architect does his job, and it’s rigidly built into the application. If that isn’t exactly the way you like to think or do your job, too bad. SketchUp, on the other hand, is a general modeler that gives you the freedom to do whatever you like. It also means more work to figure out your own working method.
A programmer friend of mine some years ago made a comparison between Pascal and C++ which I could steal to compare BIM and SketchUp: With BIM you’re constantly asking, “Please let me do this, please let me do this?” while in SketchUp you’re constantly saying, “Ooops! I’m sorry I did that.” But at least it let me.