I have attempted to repair with Super Fil from ACS but am not content with the "smoothness" of the repair. I recall reading somewhere that this is a "rough filler".
A really small blemish like a smiley can be filled with almost anything. An epoxy base filler will have higher bond strength, but cures slowly. Polyester base filler can be sanded much sooner (a little as 15 minutes), which is why polyester dominates the body shop business.
Roughness, as I think it concerns you, is a function of the filler solids choice, not resin choice. The two major ingredients are microballoons and talc, with a long list of minor players. Micro is tiny hollow spheres, so grain size is larger than talc. Among thick, prepared fillers, a high percentage of micro means less weight. A higher percentage of talc yields a filler which feathers a little better.
One roughness concern is self-inflicted; it stems from mixing technique. Micro is usually poured into a cup of epoxy and mixed with a stick. Stirring tends to fold air into the mix. Prepared fillers are better mixed on a board using a "wipe and scrape" method with a squeegee to avoid entrained air. Because they are thick, prepared fillers mixed by stirring can hold a
lot of air. Later sanding opens all the voids and the surface can look like the moon.
Nothing wrong with SuperFil, other than being a very expensive way to apply dry micro. Mixing your own is far less costly and you can control everything, notably viscosity and filler material. In this particular application (a very small dent in an aluminum surface) I'd probably use wet micro (just barely runs off the mixing stick) over sanded and cleaned aluminum. The lower viscosity lets the air escape, the higher resin percentage feathers well, and I get the better adhesion of epoxy.
On the other hand, if I was prepping for a paint day the next morning and discovered a missed smiley, well, rather than lose the day I'd grab the polyester glaze and fix it before heading for bed.
