I've been on RC for both Melges 24's (US Nationals) and Ultimate 20's.

The U-20's are nice boats. They are essentially a 3-person dinghy with a huge assym. spinnaker. You can't buy a new one (yet) since the molds were destroyed in a fire a couple of years ago. Reportedly, a new builder is gearing up to produce them again.

Ultimate Sailboats was founded by Jeff Canepa, one of the early Hobie 14 hotshots (Worlds & National Champion).

Melges 24's are 4 to 5 person dinghies. Expensive. The fleet is highly competitive - they have pro and Corinthian divisions. The hiking position (leaning over the loose lower lifeline) is uncomfortable at best.

Both these boats are athletic (roll tacking, hiking) and appeal to a younger (20's & 30's) crowd. Like all dinghies, they are extremely tactical and boatspeed differences are minimal.