Depends what you're fighting. Hive / Cabal = invective. Fallen = FV. Invective is better for burst damage cuz it fires twice as fast. You'll also never run out of ammo for invective and you can use it as a primary. Can't say the same about FV. Both are great, but if i'm not using Gjallarhorn and i'm in a shotgun mood, I'll choose invective / LoW / 4th Horseman every time over FV.