Hmmm. I'd have to say "all else being equal" the sloop is the most efficient overall - as far as powering the boat. They cost more, are more complicated than a cat, but are well understood and easy to tune. When was the last time you saw a catboat in the America's Cup?
Least imaginitive and boring to look at, but it goes to windward better than any other rig. Crack it off the wind a bit and it becomes less so.
But look at that big head-cracker boom you need for most cats (the sub 20 footers not withstanding). I had a Gloucster 11 sloop - about as small as a sloop goes - and it was a great little sailing boat.
About the best sailing cat boat I can think of is a c-scow. They don't point all that hot, but they tack almost instantly and there is no delay in running the jib in so they can hold their own in upwind duel.
Charlie P. Mud Hen 17 #69 Mad Hatter
To travel hopefully is a better thing than to arrive - R.L. Stevenson
I suspect that, if you should go to the end of the world, you would find somebody there going farther . . . - H.D. Thoreau