If it's BTB or something else with vehicles, Shield. No vehicles, Thruster.
Due to the state of the game however, you're probably better off with the Hologram. The misdirection it can create is fantastic and few things are as satisfying as watching an enemy using a Boltshot get fooled by it.
it is bad because 1 v 1 vs a smart player it is extremely easy to counter the shield. at best it just gets you back a shield safely when someone gets the drop on you and the rest of the time it gets you killed.