Without knowing more about your rig it’s a bit hard to be very specific. Is this for live use or recording in studio or both? If you have no other fx gear usually a bass player will have a compressor of some sort and then a chorusing and even distortion effect. All to enhance dynamics and thicken tone. The H9Max can do all this and more, but is a hefty investment and there might be features you’ll never use depending on the music you play and eagerness to get crazy. I’m inclined to say the Micropitch would be a good start of the three. Mainly because it’s a newer Eventide product and affordable. Although the Pitchfactor will give you more editing capabilities. Same with the the H9.
Maybe describe more about the type music you play and the situation you play most. Also, how technically inclined you are or want to get. The other thing about the MicroPitch is it was designed to be easy to use and get great sounds right out of the box. I have the H9Max and love it. If I didn’t have anything and didn’t want to spend a lot cash the Micropitch would be a top contender.