Best Octave Pedal to Get Low B up to E- on a Four String Bass

[Rockin Mike]

Gain and tone are big factors in getting an octaver to track well.
With the right input signal, my Line 6 M-series tracks very well.
It also has a mix knob so you can blend in as much of the unmodified signal as you want. This helps preserve your tone. I also has other variables (I forget which) so it's pretty versatile in getting the tone you want.

An added consideration is that the octaver is only one of about 100 effects builtin to the M-series ranging from various fuzzes and overdrives, to phasers and flangers, envelope filters, reverbs and echos, compressors, and it has a good looper too.

[Rockin Mike]

I sold a 1st generation Digitech Whammy WH-1 pedal in favor of the M-13's octaver.
Those Digitechs are craved as great octavers and I sold it for more than my M-13 cost new.
I don't know about guitar, but on bass the M-13 sounds way better to me.

[pauliebass]

Octamizer +1

[anton72]

When I used octaver it was EBS Octobass. Now I just have two 4str basses, one of them with standard tuning, the other is 35" scale with BEAD, Spector Euro 435. It sounds killer but I use only occasionally, most staying with my "regular" 4str.