I really like the Famas or Jackhammer, but i'm just awful at the game anyway so whichever gun helps me in the slightest is my friend hehe.
I mean, it has to be the AK47 in my opinion. Crazy damage, if you can control the recoil. Unstoppable at close range, good at medium range, and when that fails, Silenced Pistol/Dragunov for long range.
I enjoy the Colt 1911 for it's history, however on our servers the damage output is real. The Flare Gun is love, I thoroughly enjoy burning people alive and listening to their screams as I sit in the back of the map giggling knowing they have NO PROOF! How can I forget the AK-47 for it's sheer amount of destructive power? Point, click, repeat.
The ACR is the best. It was extremely high fire rate, and high damage. 2 Shots to the head are a sure-kill, and 4-5 to the body is lethal.
the PDW is a great weapon if you like control and critical damage. however it lacks the time to kill that weapons like the shotgun,or the AK-47. in the end it comes down to preference and play style, if you like aggressive, loud and proud game play, go for something like a shotgun (they all have their place) or a higher damage rife like the AK-47, however if you're like me and like to spread confusion you should try something with a bit less DPS and a bit more accuracy. (if you can hit someone in the head your base DPS is almost meaningless) if you like a nice balance, or even something that's just easy to control try something like the scar-H or the aforementioned PDW.
I liked the PDW, AK, and HK are all great guns, though I aim for the head so these guns can do quite the damage. Honey Badger isn't bad either. I prefer the three above though. They just have a bit more kick and range and when you get the kills going people have no idea what is going on. AK's draw a bit of attention. PDW and HK are a bit less used and not heard as often, so people won't 'Know you killed them' by the sound of your weapon and claim they 'saw you' as often.
ak 47 and the colt, although i have recently fallen in love with the PDW. I've used the ACR and the honey badger before, both are great guns. Also, the hk sl8 is pretty OP. Out of all the guns that can 1 shot headshot, the hk sl8 has the fastest fire rate and a scope and the largest magazine.
A lot of people (while I am on the server) really seem to like the double barrel. Personally I find that the colt and either Rifle, or the Hk sl8 I think it's called.