Full Idea
The leading rivals to a theory of universals are resemblance or natural-class nominalism, or sparse trope theory.
Gist of Idea
The main rivals to universals are resemblance or natural-class nominalism, or sparse trope theory
Source
David Lewis (Comment on Armstrong and Forrest [1986], p.110)
Book Reference
Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.110
A Reaction
If that is the complete menu, I choose resemblance nominalism. All discussion of properties in terms of classes is wildly misguided (because properties come first). Why not 'natural' tropes?