It would be a difficult decision to choose between a small filmy fern and a small Asplenium, as ferns go those are my two favorite groups. Although if you threw in a small Elaphoglossum, a Moranopteris, or a Cochlidium that would definitely create a problem.
When it comes to small Aspleniums, the fact that they look like miniaturized versions of a more classic type of fern is what always gets me. And while some have more simplified fronds, others are just as intricate as their larger relatives. I also like that many of these smaller ones will reproduce by sending out very thin runners and a new fern will develop every few inches. This creates a beautiful colony of ferns in time. These small ones always seem to be epiphytic, and these colonies can cover entire branches.
This small Asplenium species from El Cope is not the tiniest with fronds about 2 to 3 inches in length, but it is still a charming and amazing one.