Single Player wise almost any AR will get the job done, but in MP the only two worth a damn in terms of raw dps and ease of upgrading to X are the Mattock and Phaeston. The rest are either used solely for flavor, fire rate, personal preference or managing a 200% cooldown for ability spam heavy classes. IMO if you have to smother a gun in mods and equipment to balance it out/find a use for it then it's trash.
I agree wholeheartedly that if BioWare doesn't get back to buffing the entire roster (besides only their obvious favorite - Mattock) then the next DLC needs to provide three new ARs.
what's sad is the collector AR is a great AR...but currently it seems impossible to upgrade it. not even redeeming a 2nd code for it has worked. I really miss using it, but level 1 and level VII + for most other AR's out perform it on Gold. I still use it on Bronze when I'm leveling up a single digit character just for fun.
I think the AR's are fine, the soldiers are the classes that need the most buffing when using wpns be that a higher dmg bonus, more strength, and/or more shields/health. I really don't know since soldiers can be fine with any wpn layout just lackluster compared to all the other classes w.out proper support. Maybe a soldier buff would be a squad bonus. For every soldier in your squad all soldiers gain a +X% bonus to their wpn damage, or something. Shep and a few other iconic videogame soldiers seem to be the only soldier(s) that can do it solo, everyone other soldier seems to be most effective when there's an entire line of them.
two things i've noticed...the final evolution of Soldier's A_Rush give 100% shield cap back, but it seems it gives you 100% of your unmodified shields back, much like Geth Hunter Vision lowers your shields by 50%, but if you have their version of Fitness the shield bar goes down only about 35%ish. I suspect this is also true with Energy Drain as sometimes I've seen my shield bar go up 1/2 way and sometimes to 100%.