With the cost of arrows being too high for the average archer to always afford I suggest the following.

NM/RAID Events: Use the Best you can get, atm I consider that silver
Farming: Use warped arrows, if your farming the mobs are likely lower than you and the damage difference between warped and silver is not worth wasting the silver for farming.
Behest: Use Warped, there is so much damage going around the extra damage from Silver is not worth it. Exception: If the behest is shortmanned (during off primetime hours) you may want to use Silver or if your running with friends LS mates, you want to use your best.
Static Groups: Use your best, your likely going against hard mobs to get the most SP you can.
PUG Groups: Again use your best as your likely fighting the hardest mobs you can kill fast and the extra damage adds up. You also don't wanna be the player who only used warped arrows.

Really, its all situational on which arrows to use. I always suggest a few stacks of warped with you at all times, just in case you forget to restock or can't find better arrows on a retainer when you need em.