I hadn't really given the favorite character angle much thought, but then like you said, it really depends what they release. And I'm not sure that my favorite 3 characters would go well together to represent the series.
Maybe they'll release one figure I just can't pass up, but in the case of more ensemble productions, I've kind of tried to incorporate multiple characters into my existing displays. Or at the very least a fitting scene for very iconic single figures (James Bond displays for example). I can't think of only a single display I have now where I've thrown this out the window, and mainly because of a couple of really cool scale accessories. Henry Jones Sr. Originally intended to be in the same display as Indy along with a motorcycle, I just loved the way the clothing looked and fell in love with the idea of a 1/6 wooden desk, that I had to have him on a shelf alone - not to mention I felt guilty keeping the DX05 altar and backdrop hidden in the box.
Have I also mentioned I'm running out of space to have scene-oriented displays? I'm still eagerly following this and other ThreeZero releases to see what they have in store.