i own an oc2, dod octoplus, ebs octabass, MXR bod.
They all have their own foibles and features.
the oc 2 doesn't often come out, as i find the tracking a little iffy, but equally love the sound
octoplus - my go to octave for ages, the only one i found with a tone control for the odctave ( others use switches for setting the range of the octaved note), great warm sound, set well, it will track really well.
EBS - really clean sound, can get synthy using the switching options, but i found it too clean for my current needs. I'm sure it will return for other projects. it terms of sound, think Earth Song by michael Jackson
MXR - Love this pedal. Has the gritty sound of the oc2 available as the Growl control, and seemingly cleaner option with the girth knob. it's great to mix these two distinct voices together to create anything from subtle thickening to almighty God like walls of massive. Size wise it's awesome (although similar size to the ebs). Has a mid boost switch which really helps in a band mix too
I've also spent time with the EHX octave multiplexer. Sound great sounds to be discovered here. well priced, has a great vintage-y vibe to it. well worth the relatively meagre asking price IMO.
As always try before you buy
hope all this lot helps