I love Octavers and my favourite is still the OC2 I used one for many years until it was stolen. I then tried the EBS which I loved, it's very clean and smooth with a great sub tone and tracks brilliantly! Not a very synthy sound though. I then had an OC3 which was ok but just didn't sound as good as the OC2,it did track well though. I then got the Aguilar which just has a fantastic tone and tons of variation, I loved it. I did find it didn't track as well as the Ebs ,it's a big pedal too.
I went back to an OC2 and instantly went "there's my sound again" as I primarily use octaves to emulate synth, I then very foolishly traded the OC2 π
I currently have an EBS and is forgotten how good it is,very deep and smooth,I was about to buy another OC2 to compliment the Ebs when Simon's excellent video persuaded me to buy a COG T16! It's now my favourite octave. Absolutely great tone and very versatile with the filter (it sounds amazing with my wonderlove) it tracks really well,gets very close to an OC2 tone and it's TINY!!!!! I'm now considering a custom cog T47 now as i love it. Settled on the cog and Ebs for the mo but I still plan to get another OC2 as every bassist should have one π
I've never tried the MXR or 3 leaf but they are on my list to try,I've read that the MXR is very gritty and aggressive,so that would sound great in certain situations,the 3 leaf sounds amazing on demos but it's sooo expensive.
Anyway good luck with the search,Probably best to buy all of them π