I've owned five 12-strings. I still have an old Yamaha SA-20 hollow-body electric, and a Washburn Festival Series electric acoustic.

I think the best one I ever had was a Daijon 12-string acoustic that I added a Shadow piezo pickup to. Amazing sound, and really good intonation. I still miss it.

12-strings have a unique sound that is really satisfying as a once-in-a-while thing. I sold all of the 12s that I had before, because they were my only guitar at the time, and the 12-string sound gets annoying as a steady diet. Part of the problem is that the octave strings can not possibly be intonated correctly because the proper setting for them would be wrong for the main strings. So tuning is always a bit of a compromise.

Another thing is the need to tune in D (not E) and use a capo on the second fret. This will prevent the string tension from pulling the belly of the guitar up, ruining the instrument. But it also shortens the neck by two frets.

I love 12-strings, and I'll probably always have at least one in my arsenal, but I will also always have some 6-strings to keep them company.