Traditional pound locks are sections of canal connected to two different water levels, with gates at each end. A boat sails into the pound, the gates are closed behind it, and valves are opened. The water level in the pound changes, and the other set of gates is opened. It's effective, has few moving parts, doesn't require much of an external power source, and usually doesn't fail catastrophically. However, it requires a lot of water.
With a lift lock, the boat sails into a bathtub-like container. This container is raised or lowered to the height of another waterway, and the boat sails out. If you raise one boat-filled container while lowering another, you don't require much external power. The water consumption is nearly zero. However, there are more moving parts, and the suspended container filled with water and boats can fail in interesting ways.
The caisson lock is really interesting. A boat sails through the rear hatch of a submarine half-filled with water. The submarine seals its hatch, dives to the bottom of a pit, and locks its front hatch to a portal exiting into a lower body of water. The boat then sails out the front hatch. Water consumption is nearly zero, there are few moving parts, but it can be exceedingly dangerous for anyone in the vessels during transport.