I'm following this thread closely as this is an interest of mine, too. Out of necessity, my collection is and will have to remain small (both in number and plant size), which means I will have many months of the year with no flowers. Attractive foliage will somewhat make up for that, so I'm trying to get some ideas. And, of course, "best leaves" is all in the eye of the beholder, and I'm sure we all have varying ideas of what we like.
I'm especially attracted to mottled patterns, so I'm very happy with my new Paph. delenatii. Jewel orchids are also on my list, as jkofferdahl mentioned.
I'm looking up all of the suggestions here for more ideas!