One way to minimize immersion is to raise the lift whenever you're going out in your boat. Older lifts with exposed drive shafts are unsightly and can pose a danger if people's fingers get too close. Open tops allow rainwater to rinse off the drive shafts and cables, but do not protect them as completely. Look for grooved, winding sleeves on the drive shafts. They keep the cable from spreading or overlapping on the shaft.
Some lifts have spanner beams on the lower cradle to stiffen it.
Other points of comparison are the drive-shaft bearing system, adjustability, maintenance requirements, product liability insurance and warranty. One is the low-profile HydroHoist lift, which will accommodate boats up to 30,000 pounds and eliminates the need for pilings. It rises and falls by forcing air into, and letting it out of, submerged tanks. It's suitable only for protected waters, as is Sunstream's underwater hydraulic lift. Most manufacturers offer accessories for their lifts.