The best perks in Call of Duty: Ghosts are those that give you more damage, help you stay hidden and give you an advantage in contested firefights.
The reason I am making this post is because a number of people, both on YouTube and my website, have left feedback about what I said about the Armor-Piercing attachment in Call of Duty: Ghosts.
You can gain more perks in Call of Duty: Ghosts by choosing not to use some slots. Each of the primary weapon, secondary weapon, lethal and tactical slots gets you one extra perk point. Note that not choosing a point streak will not gain you extra perk slots.
I found that the AK-12 is the best gun in Call of Duty Ghosts. The maps are fairly large so naturally the assault rifles have an advantage over submachine guns. Also, if you are ready for enemies, the AK-12 is very powerful at close range and can easily keep up with submachine guns.