A manual chair is best for nearly all ports. You can take a manual chair on a tender, but rarely a power chair. In addition, there is a scarcity of ramps and curb cuts in most ports, so you will have to bump up and down a curb or step or two. Most ports have no accessible transportation, so you would need to transfer to a cab and use a folding manual chair to go anywhere.
I don't know of any cruise ships that use anything but a ramp for docked ports. No lifts, and the ramp can be very steep and bumpy.