Probably MOST important is location. It has to be in an area where bucks feel safe visiting it during shooting hours for it to be of any benefit to you. Near bedding areas for late afternoon hunts is preferable, and will take some experimenting. Later in the season, make them near existing scrapes you find or simply take the deer made ones over.

Best bet is probably basic buck urine, or synthetics like Hawgs Unlimited or Robinson Labs...

Or your own urine. Just read an interview in this months Bowhunting World with Mike Weaver (I think that was his name). He has more P&Y entries than anyone, and he urinates freely when he hunts, even uses his own pee to freshen or open scrapes and consistently kills several big deer each year.

Urine is basically Urine. As long as you don' t contaminate the area with non-urine smells (like smelly pubes), I don' t think it makes a difference whether you use yours fresh or from a bottle you paid for...