I use power chords when they're called for, and full chords when they're called for. Sometimes a simple power chord is all that's needed (and desired), whereas at other times you need a richer chord to get the musical message across. I'm a big fan of ninth chords, and suspended second chords, as well as tritones when that certain dissonance is what I'm after. Thinking about it, I guess I don't use as many power chords as I once thought I did. I play a lot of things that sort of feel like power chords, but are in fact a variation on them, or something totally different altogether. And then there's the other way: just using single notes from time to time. Chords can be mis/overused, and can detract from the feeling or power that a single note riff/melody would bring. Then, to step it up, two-note harmonies are often an even better change of pace from chords, because they're the middle-ground between single notes and chords (three notes or more, obviously). Eh, I don't suppose this was a very helpful post... but hopefully, I said something along the way that made some sense. =P