Use whats cheapest. Poly fill may require changing a bit more often as it's more "dense" but that said it will filter finer particles sooner due to loading up faster.
Unfortunately, the dirtier a filter is the better it's working clarity wise, but this also leads to more necessary filter servicing. Pick your poison.
I myself shoot for longer filter servicing intervals (3-6months)and use less dense foam, and my water is still crystal. This can also be contributed to how mature your tank and filter is, and ow often you do water changes, along with what and how often you feed.
Of you seem to find your filters are getting gunked/slimed up frequently, you are probably overfeeding, or extremely overstocked.
Remember, feed your FISH, not your filter....
HTH