Conclusion: The Revenant is the best rifle at close range. The Geth Pulse Rifle is an inferior assault rifle in terms of damage per second, except that it does slightly more damage to shields than the Avenger. The Vindicator is superior to both Avenger and GPR. The only reason to prefer the GPR over the Vindicator is 1) if you're worried about running out of ammo and 2) like an assault rifle that's more accurate than the Avenger.
Class: Infiltrator (17) (used savegame editor to get the Revenant) 2/5 Assault Rifle Damage upgrades, no Assault Rifle Penetration upgrade.