Lucky bolt: very very lightweight nearly no kick, allows for a slight reduction in dwell time slightly increasing efficiency
Firebolt: Slightly heaver so more kick, but used in combination with the stage 2 and 3 from lucky, will wield the best results possible (out of all the bolts I know of) in terms of efficiency and lowest dwell times
Personally I would go for the lucky bolt due to fact that it reduced the kick to practically nothing and they have fantastic customer support but neither are a bad choice really
-Mat