First off, let me preface what I'm about to say with the fact that I don't have a Saber, so I won't comment on it. Same goes for the Collector Rifle, but that thing according to all feedback is absolute junk.
This extends past AR's. Automatic weapons in general are bad.
You can claim that I'm a fool, but coming from Battlefield 3 and Modern Warfare, the only Assault Rifle that functions as one is the Harrier. It is strong damage. The drawback they have built into it is its diminished ammunition capacity so you spend more time humping an ammo crate and most of the time it simply isn't viable in Platinums when you have 2 banshees, 2 primes, and 2 phantoms dancing around ready to scramble your face while you run to refill your ammo.
My opinion is as follows:
Top Tier:
PPR: Boss killing AR, drawbacks are obvious. Nasty gun if you are good dealing with its mechanics. Personally I'm not. The biggest drawback is its range, honestly. While its damage is very strong when ramped up, the class that works best with it (Destroyer) doesn't worry about cooldowns, so you have a Piranha, which when accuracy and clip-specced is nearly redundant on range and actually benefits from hard cover usage by tightening its spread even more.
Harrier: With the Demolisher, this is an outstanding gun. Its damage is very strong. It behaves like an assault rifle should. It's the equivalent of a M5 in today's terms. Accuracy is great enough to snipe with. Ammo drawbacks are bad. Can be a great complementary weapon for longer range Atlas-Crotch removal or something like that on say a vorcha or Krogan, but tough to use as a main weapon.
Indra: Hip fire penalty is a major drawback (how the hell does aiming down sights increase damage per shot?) but this is a powerful gun when the scope isn't a hindrance.
Hurricane: Here lies your most powerful fully automatic weapon. Stability damper and Clip or Heat Sink turn this into a similar damage-to-harrier gun with higher capacity and slightly less accuracy at longer ranges. With ULM combined with a Pistol, this thing can be amazing.
Best of the Bunch: Hurricane
Worst of the Bunch: Indra (hipfire penalty is unneeded, scope is punishing in many cases) As my buddy said, it needs its category changed to AR and the Saber needs swapped to SR.
Tier two:
Here you have purpose-driven guns:
Striker and Falcon: These are defensive weapons that can set up bursts and limit a lot of possible incoming damage on a squad. Their ability to stagger is amazing for supporting your team and allowing them to headshot everything. They can insure that your biotic abilities like Warp, Throw, and Pull are not dodged since a target will be stunlocked prior to power usage. The AoE ability to spread ammo powers can set up bursts gallore.
Revenant: Personally I don't see how people use this outside of Marksman, Hunter mode, or Devastator mode, which is really where the gun ends up being pretty strong. It is relatively available, too making it pretty damned good in the right hands. It's a limited niche.
There's no best/worst here. These are specialty weapons.
Tier 3:
Here's where we're getting below the Mendoza line outside of the Mattock (which is semi Automatic).
Mattock: Semi-auto, great gun for limited manifests or lighter weight applications but once you get a Carnifex or Paladin, there's simply very little reason to use it. The Viper is in the mix here, too. I used it religiously until I got the Harrier. Carpal-tunnel city.
Phaeston/Avenger: If find these two very similar, honestly. The Phaeston is a slightly upgraded Avenger, which actually was borderline overpowered for a common until the Stability Damper was released for SMGs.
Tempest: It's a diet Hurricane. Shoots a little straighter baseline, but less damage than the Hurricane. Not bad. Stab damper made this thing pretty solid.
Hornet: If you have a Stability damper, this is a very strong and accurate little gun. Slots somewhere in between the Hurricane and Tempest but again, Carpal Tunnel. Very good for casters due to light weight.
GPSMG: So here's my first fully auto weapon that I started using over the Mattock. Shoots straight as an arrow, and for some reason this little guy is outstanding against armor. Ramp up is a bit of PITA, but nowhere near as bad as the PPR and the shots don't gain damage as far as I know after ramp-up. It simply gains firing rate. It gets special mention since its the only SMG that benefits from ULM without a ULM Pistol equipped, too.
Best of T3: Mattock. Damage-to-weight ratio is strong. Wrist health disaster is not.
Worst: Phaeston/Avenger: Outclassed by the SMG's in here.
Poop Tier:
Geth Pulse Rifle: Gives you a rash. Damage is below trash. No stagger. This thing needs much more love to not be crap. I don't care if its weight needs increased. It is worse than the Phaeston and Avenger and they already fill the slot of being lightweight, accurate, and having decent ammunition capacities.
Typhoon: I mean, UR, weighs as much as a house, terrible against health, redundant in its purpose with the PPR, which is lighter. WTF wai nerf?
Locust: Somebody please explain to me why it even exists.
Eagle: Lol. Would be killer if you could eradicate your foes with hugs. If they nerfed this gun one iota it would heal your foes and one-shot you.
Shuriken: At least it's a starter gun...........
Vindicator: Honestly, this thing isn't that bad, but I'm going to underrate here and admit I did so. It needs a burst RoF buff, an accuracy buff, and a weight buff. Its damage isn't bad. Biggest issue is that its a 3-burst semi-auto and doesn't really serve a purpose at all. With those changes and possibly a further damage buff, this could be a pretty cool gun.
Bottom line:
Guns should have been balanced downward from the Harrier, not upwards to it.
What I mean by that is that only the Harrier truly functions like what most people would expect an Assault Rifle to be. It has solid stopping power, good accuracy, and weighs as much as you would expect.
There's a rather large hole between the Harrier/Hurricane and the next automatic, and it legitimately should be populated by the Geth Plasma Rifle as it is a Rare or a more accurate Revenant. You can argue that the Mattock fits that slot, but the gun is punishing to your health to use or requires a turbo controller/key macro.
My suggestion is this:
Release the Blood Pack SMG next week. It fixes most issues since it hits that niche of having good ammo capacity and doing damage more in line to what full auto weapons should.
The ADAS would also be interesting for Adepts and Vanguards. Just keep it lightweight.