Snapshot Vs Rapid Shot

I'm not sure of how these two traits work.
Should I pre-shoot in aurore beret and fire in navarch's hat? Or should I just keep the tricorne all the time for shooting?

Snapshot is essentially the equivilence of haste for ranged attacks, lowering the base delay by a certain % based from your ranged weapon and ammo.
It is invaluable for ranged attacks for the same reason haste is vital to melee attacks.
Rapid Shot however is a base % chance of having your next ranged attack be instant cast/zero delay.
I would assume that as awesome as Rapid Shot is, it would have diminishing returns rather than cumulative effects vs Snapshot. Similar to Double Attack vs Haste.

tl;dr: Snapshot is consistent delay reduction that is cumulative. Rapid Shot is instant cast ranged attacks, but is inconsistent due to random, percent based activation.

My recommendation is to use high Rapid Shot activation gear for pulling and save Snapshot for consistent DD shooting.