What combination of Revit software will give the most with the least outlay of cash with the current Autodesk product delivery strategy? I believe that the answer is Revit Structure (RST) and Revit MEP (RME).
These two versions have all of the features that Revit Architecture (RAC) has spread between them plus there are compelling extensions for both whereas RAC has simply inherited its own from them.
It isn't really a coherent work flow to travel between the applications to do your work if you are an architect. As an example, you can't make a ceiling plan in RST but you can in RME. You'd have to use RME for full documentation purposes, not RST. At the very least you'd have to travel back and forth.
You might not even consider it efficient if you aren't. It would be more slickerer coolerer, Sweeterer (my opinion) if it were one seat of Revit that provided all the tools but that was a different post.
Schedules in RME offer both conditional formatting and embedded schedules, very useful and potentially interesting in that order. RST offers Graphical Column Schedules while RME and of course, RAC don't. RST also offers more tools to provide more accurate structural conditions like beam coping and curved beams.
Deployment would be a bit of a pain because you'd have to download the RAC content from the Autodesk web libraries and setting up templates might be a bit of a pain since you'd have engineering templates to work from instead.
I've experimented lately with not using RAC and favoring just RST/RME to see when I bump into something insurmountable, so far I haven't.
Perhaps Autodesk would recognize the value of a combined version if RME/RST sales began to cannibalize RAC sales? I was told that my earlier survey heavily biased the result by how I wrote the choices. I suppose but then what survey doesn't have a bias?
Something to consider. As usual be sure to prove it to your self satisfaction...your mileage may vary! Buyer beware...reader beware!