I have heard the poly lift spin, and they are more expensive. I think all three (hydro, galva, and poly) are very similar, built like brick ****houses and a thicker brick ****house may not be required or worth the extra money - however, the non carpeted bunk may be worth investigating.
We have one (Galva) on the main channel LOTO 14 MM, spent 3 years with no protection from the wave action and the last 2 with some wave breaks protecting the docks, no problems yet. We used the rough water kit - prevents constant up and down motion by locking the lift to the dock. Poly does not offer this option. This kit is potentially harmfull to your dock if it is not set up correctly because you will try to float your dock with your lift. If set up well, I think a rough water kit is the way to go because it reduces wear on the joints and reacts the side loads that can otherwise bend the arms.