i've owned both the OC2, and OC3 and a micropog.
I personally prefer the Octave down sound of the Boss pedals (my jap OC2 had amazing tracking too, dont really remember the OC3 that well), its alot fatter, like the bass notes on an electric keyboard (IMO), while the Micropog seems a bit thinner tonally and very digital - sort of like your bass but with no soul like its being run through a chain of compressors, bad compressors. HOWEVER, it does UP and DOWN, and tracks perfectly and polyphonically, and altho i sold my last micropog, it was only because my guitarist fell in love with it and insisted that he buy it off me, however, i should have a new one within a week or so. And i cant wait.
The fact that its polyphonic and tracks flawlessly (to me anyway) cannot be overlooked, and also i feel that having an octave up rather than -2oct is far more useful. even if you hate the oct-up, you still have an octaver that doesnt care where you play, what you play, or how fast you play it.
so just for standard octave down id go for a Japanese OC2, but you have to be careful where you play (not too low) and try not to do any double-stops or chords
if you want to turn a 4-string bass into a 12-string get the micropog

it completely eliminates any GAS for a 8 or 12-string (admittedly the GAS was minimal, but it was there)