9. BAL-27 - Advanced Warfare
The BAL-27 was one of the first weapons you had access to in Advanced Warfare, and for most players, the game never really gave them a reason to stop using it. A reliable assault rifle with a high rate of fire and little recoil, where all of the other weapons in the game had their pros and cons, the BAL was pretty much just all pros.
The worst part though was that, thanks to the increased mobility, the lack of any substantial recoil and a steady line of fire, the gun could annihilate players from pretty much any angle. The devs were still figuring out how to balance the newly agile movement system with the accessible weapons the series relied on, meaning that deaths often felt cheaper than they would have in other games.
Pretty much everyone was using this weapon when the game dropped, and it's still one of the most popular choices (even after a patch lowered its efficiency) if you jump back into the title today.