What you've asked is essentially, "Which is best? Hammer, screwdriver, socket wrench, or welder?"
Each of the items you listed are specific tools best suited to much more specific circumstances than you've...er...specified. I've used each, and will continue to use each in the situation best suited to the tool. The trick is to learn the appropriate circumstances for each.
I prefer Isinglass for fining English-style cask ales. I prefer gelatin for fining beers that won't clear by patience and cold. Isinglass will work multiple times if the beer is roused; gelatin won't. Polyclar has an opposite ionic charge than Isinglass, which makes it useful if used in conjunction with another fining agent. Hell, if you're doing fruit beers, you forgot what many consider a fining agent: pectic enzyme. The list goes on.
Yes, there can be a cost/performance/PITA tradeoff. Isinglass can come in a variety of ways, for example; the least expensive requires a level of skill and process involvement that can quickly become a PITA, but the most expensive is the easiest to use.
Whirlfloc is essentially highly-processed Irish Moss. It's technically a kettle coagulant, not a fining agent, because fining agents are used post-fermentation. I agree that Irish Moss added to the end of a vigorous boil will improve clarity. Of course, this assumes you're already aggressively chilling your bitter wort; all the Whirlfloc in the world won't help a beer with piss-poor cold break due to poor chilling.
So the short, glib answer is this: No one ingredient is "the best". They've all got different uses. Your job is to learn what those uses are.
Regards,
Bob