Basically, I'm a big fan of this game, in particular multiplayer, and wanted to give my two cents on the available weapons. I own and have used almost all of them (special pre order weapons like the collector rifle discluded) so I feel most of my opinions are credible and mor the most part original. Let me know what you think/ if you disagree with my analysis of certain weapons, please respond. Also, apologize for any typos or gramatical errors. There will be some.
** denotes a gun I do not have
Rare Level- Common
M- 8 Avenger- The avenger is the standard issue assault rifle in ME 3, dealing low damage, and having an average thermal clip, but boasting good accuracy, very low weight, and a fast reload time. The Avenger is about as standard as it gets. Personally, I preferred it to any of the other starting weapons, but quickly abandoned it once I unlocked other assault rifles (nearly all are preferable). On bronze and silver difficulties, it can be useful when paired with another gun or with a power dependent class due to its extremely low weight, but dont even bother on gold.
Rare Level- Uncommon
M- 15 Vindicator- The Vindicator is a three shot burst rifle, but is otherwise fairly similar to the Avenger. It deals low damage, but has good accuracy, weighs next to nothing, reloads fast and has good range capabilities. If you can manage consistent headshots, it has a higher damage output than the avenger, but it is weaker on the move and at close range due to its burst nature. The Vindicator always reminds me of the battle rifle from halo 2, incredibly standard. I always favored the vindicator in campaign, particularly ME 2, but there are better options in ME, particularly for multiplayer.
M- 96 Mattock- The Mattock is a semi automatic rifle dealing good damage per shot, high accuracy, less than average weight, and having 16 shots per clip standard. The Mattock is a very useful gun for many classes because it both is accurate and deals high damage. If you can consistently land headshots, you can dispatch even shielded enemies quickly. It works great with the scope, thermal clip, and damage mods. I particularly liked this gun early on with the asari adept and vanguard, as you could freeze enemies with stasis and then repeatedly headshot them. Frankly, I found the Mattock to be one of the better assault rifles above even some of the rare ones, a skilled player can make great use of it, especially in combination with power usage.
Rare Level- Rare
M- 37 Falcon- The Falcon is a semi automatic rifle that fires mini grenades. It does good damage per shot, has slightly higher than average weight, a slow rate of fire, but deals splash damage. Despite its cool name, Im not a huge fan of the falcon. While the splash damage and staggering effects are nice against groups of weak enemies, it simply takes too many hits to kill considering it fires grenades. It also fires very slowly, and more often than not, some douche teammate will steal your kill(s) while you are in between firing shots. It also is surprisingly useless against big enemies like banshees and atlases. It can be a fun gun to use when coupled with powers like adrenaline rush, marksman or devastator mode, but dont expect too much from the falcon, because it simply wont deliver.
M- 76 Revenant- The Revenant is a powerful fully automatic machine gun capable of shredding targets at close to medium range. It has a sizeble clip, deals heavy damage, and is about average weight, but unfortunately is very inaccurate. There are several ways to mitigate the accuracy weakness whether through a stabilization module, a gear/equipment bonus, or certain characters have accuracy bonuses. Without said upgrades, it suffers at medium to long ranges, but its power helps to make up for this. The Revenant is a fun gun to use, and when upgraded, is flat out deadly. There are other assault rifles I prefer, but this is an overall very solid one that also is quite satisfying to use.
Geth Pulse Rifle- The Geth Pulse Rifle is a highly accurate fast firing assault rifle. Its strengths include its virtually inexistent recoil, its large clip (second largest among projectile firing assault rifles), and its lower than average weight. Its single flaw is its low damage, particularly against armor. The GPR is a pretty good gun against most types of enemies; it is very accurate making sustained headshots easy, it fires very fast and has a large clip meaning you can take out multiple enemies in one clip, and it doesnt weigh too much. The damage is understandably low against health shields and barriers, but is painfully low against armor. I made the horrible mistake of using the GPR on gold against reaper, and let me tell you I had a bad time. Even at levels V-X it still is pathetically weak against armor, so dont even bother. As a result good when paired with an armor piercing gun, or with powers like incinerate/flamer/warp.
Phaeston- The Phaeston is a light assault rifle characterized by low damage, a large clip, and fast firing. Although it often times is compared to the avenger, I have found that it is fundamentally very similar to the geth pulse rifle, although it does slightly more damage, has a smaller clip, and is a little less accurate. The Phaeston is essentially a nerfed version of the Geth Pulse Rifle because even though it does more damage per shot, it still unloads much less damager per clip with comparable mods. The one clear cut advantage the Phaeston has over the GPR is that it is better in close quarters due to its spray. Its a well balanced assault rifle, especially in campaign, but in multiplayer there are better options.
Striker Assault Rifle- The Striker is an automatic assault rifle that fires explosive high damage rounds. These perks are offset by high weight and a small thermal clip. The striker is comparable to the falcon as it fires explosive rounds dealing damage to a small area. It differs from the falcon in that it is automatic, albeit a slow rate of fire for an automatic and limited shots before reload. The Striker is pretty mediocre in my opinion, able to take out a group of light enemies, but incapable of doing real damage to heavy enemies. The magazine upgrade, and powers like marksman and adrenaline rush make it more effective, but at the end of the day all you have is a heavy assault rifle that deals average damage and is somewhat hard to aim.
Rare Level- Ultra Rare
M- 99 Saber- The Saber is a single shot assault rifle dealing massive damage per shot. It weighs more than most assault rifles, but its sheer power more than compensates for the weight. Personally, this is one of my absolute favorite guns for silver difficulty, as when equipped with the extended barrel is a one shot headshot on unprotected enemies. Combine this with a shield draining power like overload or energy drain and you have an unstoppable killing machine if you can pull off the headshot consistently. One of my most favorite classes is the turian sentinel with a saber, as turians gain a bonus to weapon stability, and your powers are overload and warp to weaken any defenses. The main drawback of the Saber is its high recoil and slow fire rate, making it challenging at close ranges. It doesnt seem to suffer much if any damage reduction for hip fire, so can effectively be used when no scoping. Even on gold, this thing packs a punch.
Cerberus Harrier- The harrier is a fully automatic assault dealing high damage per shot, but being restricted by a small clip. I only recently acquired the harrier, but it quickly became one of my favorite guns, as it should be due to its impressive stats. The harrier is equitable to a fully automatic mattock, meaning that it can deal massive damage in a short time. It also is surprisingly accurate for such a powerful gun, having significantly less recoil than the saber or striker. Its main flaw is its ammo limitation. You only begin with 20 shots per clip and 80 reserve, so youll find yourself both reloading often and needing to visit ammo crates sometimes multiple times a round. It also is rather heavy, but as you may or may not know, all the best weapons are heavy. Anyway, the harrier is capable of dispatching even shielded enemies as if they were swarmers, but be prepared to camp the ammo crate.
Particle Rifle- The particle rifle fires a sustained laser beam that expands to deal more damage after a few seconds. Rather than firing rounds, the particle rifle has an energy supply that starts at 100 and drains as the fire is held down. If the ammo reaches 0 you are in for a long cooldown and reload time, so try to stop when it is near 0 as opposed to depleting all the energy. You may have guessed that the particle rifles energy depleting style necessitates the magazine upgrade, which can almost double the amount of time you can fire it. This greatly increases the effectiveness of the gun, as it is capable of killing most enemies in a couple seconds, especially when fire is concentrated on their domes. I really like the particle rifle as a secondary weapon on classes that dont rely on powers such as Krogan. It is fairly good against all defenses, and can weaken even large enemies like atlases and ravagers surprisingly quick. I wouldnt recommend it for close quarters or in most cases as a standalone weapon because for it to be useful, you need to be standing still firing for a prolonged period of time. The Particle rifle is very fun to use, but its high weight and forced exposure make it the worst of the ultra rare assault rifles.
**N-7 Typhoon- The Typhoon is a heavy machine gun that has high recoil a large clip, and good damage. While the Typhoon is the heaviest assault rifle in the game by a fair margin, it does good damage in addition to having a standard 100 round clip making it capable of dealing massive damage per clip. It is one of those guns that increases in rate of fire up to a maximum speed. Since the Typhoon is one of the guns I dont have, I cant speak to my personal feelings on it, but Ive seen players rack up kills particularly with classes like the devastator or other soldiers due to the weight tradeoff aspect.