Having been in rigs with both, here are my personal opinions.
The opti is proven and very reliable, especially in 115-150 models. Love the opti growl when cracked wide open (not really much louder than a 4 stroke, but is definitely a different sound).
The etec is a pretty smooth running motor, and actually trolls down fairly decent (for a 150). Slightly quieter than the opti.
I will say this though, after the terrible experience I had trying to find a tilt/trim for a johnson motor, I consider parts availability big time in purchases. That’s a part of the reason I have an opti and pro-kicker on order for my new rig.