Size per size... Ketches are more expensive, and have more
parts to break and/or maintain, but they allow the sailplan to be split up, making them easy to reef. On the other hand, the mizzen is often in the way if it's in the
cockpit. In my view, the neatest thing about them is the ability to put a radome and "quiet"
wind generator, up high and out of the way, (without a conflict with the jib), as well as split up
mast head clutter. Many would argue that they are more beautiful, and I think this is the main reason that some folks are drawn to them. AESTHETICS COUNTS!
A
cutter rigged
boat on the other hand, that's normally sailed as a
roller furling sloop, but with the ability to sail with staysail and reefed main, or staysail alone... would be every bit as easy to handle shorthanded, less expensive to own & maintain, less complicated, and more efficient to windward. It may well have less aesthetic appeal though, and the
mast mounted clutter must be partially eliminated or stuck on one mast. Here, the "sloop/cutter" pros outweigh the cons, and this is why Ketches have fallen out of favor with designers, builders, and buyers for decades.
It is largely a "personal" choice, however. In either variety, the good ones are wonderful, and the bad ones are a pain in the ass. I have never met someone with a modern
sloop or
cutter rig, wishing that they had a Ketch... And I have never heard of someone with a lovingly restored older ketch, wishing that they'd gone with a sloop or cutter.
It appears that we choose boats the way we choose spouses... emotionally!
Mark