My experience is that the first agent will usually point out another pilot that has inquired first. Even if s/he doesn't, I've never run into a second pilot that didn't respect the first-come-first-served rights of the first pilot.

This, of course, is not to be confused with two pilots from the same airline trying to get on the same flight, and the senior one wins.

I've been on both ends of both of these scenarios. Sometimes you win, sometimes you lose. In the end, it pretty much comes out even.

My one piece of advice if you commute from a relatively small station (or a big airport where your company only operates a few flights a day) is to try and get on friendly terms with as many gate agents as possible. Show some interest in them, bring them a snack/drink on occasion, and show some appreciation. The day will come when they get you on a flight you shouldn't be on....and if they don't take a shine to you, they can see to it you don't get on a flight that you should be on.