I couldnt find scrubbies at affordable prices where I live, so I went for a "craigslist" purchase of 300 liter of 3 or 4 different kind of plastic bio media, much of which is really intended for bakki showers (most of my media floats).
Now I would guess that scrub pads are better to filter fines out as well, but for that same reason, likely inferior to bioballs for biological filtration. If you fill an entire barrel with it, I would also be concerned about spots of standing water. Still, if you are going with a "one barrel does all" approach, scrub pads are likely your best bet. If you go for a staged approach with one barrel doing mechanical filtration (vortex/sieve/brushes) and other for biological, I think bioballs, K1 and the like would be better.