One thing is that your personal decision shouldn't be based just on what everyone's favorite is, but what you are trying to accomplish sound-wise.
My quick opinion/experiences on some of the octavers:
POG-If you're planning on playing more than one note at a time (though I find the Aguilar & EBS can handle simple intervals like octaves and maybe even 5ths without sputtering) this is the pedal you want. It's the only one of the bunch that is truly polyphonic. One downside is that it does sound a little "clinical" compared to the others, and not quite as deep.
EBS-I think this is the best one if you're looking for a more subtle octave sound-it seems to have very little character on its own, so it blends in with your clean sound really well. Good for making your bass simply get that extra "oomph".
MXR-On the other hand, the MXR probably has the most character. As Funkyebk stated, this is a good octaver for aggressive music as it sounds kind of gritty with the growl voice and punches through with the mid button engaged. Only downside is I think this one tracks the poorest. It isn't as forgiving in my experience as the EBS or Aguilar.
Aguilar-I think this one is the most versatile. With the four knobs, you can get A LOT of sounds. Turn the octave filter fully clockwise and the octave level 100% wet, and you get a nice, synthy octave sound. Fully CCW or maybe a bit higher and blended with the clean signal you can get some EBS kind of sounds.
The above is all obviously IMO, and YMMV.