ACR, hands down.
Type 95, FAD and MK14 are not useless.
PP90M1 (short range) and MP7 (any range)
Semi: RSASS and Dragunov
MP9 (any range) and akimbo FMG9 (short range)
Overall best, ranked by their effective ranges in order of preference and with a score out of 10 possible points:
ACR: Medium (10/10), long (8/10) and short range (1/10),.
Akimbo FMG9: Short range (12/10*), medium range (2/10) and long range (0/10)
MP7: Short (7/10), long (7/10) and medium range (6/10).
PP90M1: Short (9/10), medium range (4/10) and long range (1/10)
Akimbo FMG9s are capable of killing a juggernaut in 0.7 seconds, and is the the only weapon that can reliably kill a juggernaut without reloads apart from LMGs and P90
Single FMG9 matches MP5 and UMP in power and accuracy.
I think the people suggesting red dot / kick for the ACR are trolling. My fav AR is the CM901 w/ silencer / ex mags. Not really big on the SMG's, for ease of use and accuracy the MP7 is probably best, however the PM-9 is the most fun to use and quickest to kill. Sniper rifle for me is the AS50, virtually no BS hitmarkers like the MSR and L118A. Very little recoil with kick when prone as well. Best shotgun is the USAS, granted you can spam the striker but I get ten times as many one shot kills with the USAS. Secondary MP9 w/ extended mags, I can play whole games with that and not use my primary.
The best weapon in the game is a tie for me. The MP7 and ACR.
The MP7 features faster movement because of being an SMG, extremely low recoil, very good at extreme ranges, better or equal to most AR's in that aspect. The recoil is so low, that rapid fire is still very controllable for long ranges, and gives you a boost up close making it hard to beat.
The ACR features extremely low recoil, even without kick. With a silencer, it's range is barely effected and deals out a high amount of very controllable damage. A silencer with extended mags will certainly almost always beat any other weapon from medium to long range engagements while being able to take out multiple enemies with ease.
A close 3rd for me would be the MP9, as it's a laser beam and just about as good as the MP7.
I agree with Moofda. The ACR and MP7 should take top honors. That's not to say that there aren't great guns...I've used the PP90 more than any of 'em, but overall it's the ACR/MP7. I have also been impressed with the MP9 for a secondary! If we are talking best secondary, I like it best. Honestly I haven't used the FMG's much since they were so used and abused, plus it's ROF seems slow. My 2 cents.