There's a big debate within multihull circles--tris vs. cats. Tris have the advantage of being lower in the water and have the amas for stability. The drawback is that it's essentially a monohull with outriggers. For liveability, it's cramped. If there's any useable area in the space between the amas, it's just sleeping space. One would be lucky if there's enough room to sit up. Cats have the advantage of having two hulls and the bridgedeck with living area in the hulls and bridgedeck. The disadvantage is they're higher above the waterline and have more windage. Both can end up with huge design flaws--having a cat with the bridgedeck too low or a nacelle can lead to a lot of slamming. Hobbyhorsing is just a joy, too. Then there's sailing one of these babies--if someone's used to sailing a monohull and goes to a cat, they're surprised at how fast a cat (or tri) can react to wind/wave conditions. A monohull is much more forgiving. OTOH, cats/tris have a heel of around 5 degrees (give or take a few), so the ride is much more pleasant--and you have less of a risk of wearing your food. The nice thing about cats is that they can go like a bat out of hell.
We went to a talk that Chris White gave years ago. He's designer of multihulls and was a big tri aficianado. He said he loved his tri, but wanted to design and build a cat. Why? Because his son was getting older and when he'd say, "go to your room," the "room" was three feet away. I did see a Chris White designed cat at the Annapolis boat show a couple years ago. I don't know if he's built one for himself.
But unless one really knows multihulls, it's easy to make huge design flaws. About five years ago, we watched a quick & dirty boatbuilding contest in which the boatbuilders were to build a boat and paddle it around a course. One of them built a catamaran. When they launched it, the person next to me--someone who had admired our little cat--said, whadda think of the cat? I said, it's not going to make it. Why? Because they had put all their effort into building the hulls, then hammered a couple pieces of wood between them. Their failure was not understanding that the stresses in a cat-and in a tri--are in the crossbeams, because of the constant flexing of the hulls and the forces on the crossbeams from all directions from the flexing, the force of the water, the wind, you name it.
Our next lesson will be: mast compression and the catamaran. You will be tested on this material, so take good notes. :-))
CW comes very close to my perceptions of the right balance of factors in multis.
For ocean cruising, IMHO, very fit, light well built tris are best 30-40 feet. Cramped, but seaworthy and fast. Over 40 feet cats come into their own with sufficient above wave height but not too high profile. It's very hard to execute a cat like this under 40 feet.
Above 50', choose cat or tri, depending on your preferences.
(All the opinions of one with 25,000 ocean miles, mostly on our 48' steel cutter!)
Since so much of ocean sailing is in very light air, a slippery low drag tri would be very nice. Also easier to adapt storm tactics than a cat. And some distance from the main hull for collision damage, and easier to adapt to 180* living inverted!
That said, the room and trade wind speed of a 50'+ strong light low narrow hulled cat.....sigh.
And "condo cats" like PDGs and geminis don't count, they are inland coastal motor sailors IMHO.