Any gun with some sort of sight enhancement because iron sights suck on that game.
I don't mind iron sights actually. I'll play a gun in TDM to quickly unlock accessories, but will usually stick with iron sights or maybe the RDS. Yes, even the sniper rifles.
Back on topic, while the SCAR-H and UMP 45 are great guns, I still love my Remington 870 & M249 SAW.
These replys are pretty strange. But as far as my experience and testing goes. Im only level 36 in BF3, All of the weapons are realistically great and a couple of them actually feel real if not so real at least the reaction time and the reloding time is pretty spot on from a couple of the weapons. I like the AR but now im starting too use the PDW i think its awesome and quickly accurate depedning on your characters modification per weapon.
I did like the p2000 I picked up from someones corps. It was really quick and seems deadly with the fire rate vs magazine size. If you guys are old enough try going to a nice gun range and trying some of the guns for yourself. Its not too expensive and it would it IS and awesome expereince to come back home and try the games weapons again.
close to mid range: G36C with grip, red dot and silencer (I have 5 service stars on that one, lol), or the MP7 with the same load-out (it has the highest fire rate, I think).
long range: M39 EMR with 8x or 12x scope, bipod and silencer, or the L96 with same scope, bipod or straight pull bolt and silencer.
I am almost Colonel Service Star 2 and these were the most fun for me so far... But I haven't played the assault or support classes much yet, which I will start on after I get the first recon service star (after my 4th engineer service star I decided I had to try the other classes as well, lol).
With the new B2K DLC now out, the FAMAS has got to be the baddest gun in the game right now. Pretty much nothing beats it in close to medium quarters combat. I've heard that DICE will be nerfing it soon however, so enjoy your service stars on this while you can!