The AEK is one of the most popular assault weapons in BF3. It has always been among the more popular assault rifles and has suffered nerfs, attachment buffs and nerfs to other weapons that made it more appealing.
Since the release of Battlefield 3 the AEK971 has been worth using. At no point was it bad enough to relegate to the pile of average guns, provided a player learnt when to full auto + correct fire and when to burst. And also it did not really matter what setup you ran on it. Originally the suppressor or heavy barrel with foregrip was decent, then the suppressor went out of vogue and the heavy barrel was the goto for all assault weapons. Finally the flash suppressor became a useful alternative. The laser sight has always been an option but most players go for a P90 or other PDW rather than using an assault rifle in the hip firing role. This does not mean that the AEK cannot sit in this niche comfortably.
Enough prattle, what attachments should I use now with the AEK
The AEK is the only assault rifle worth putting a foregrip on. Foregrip removes horizontal recoil and adds spread on a weapon by weapon by weapon basis. On all the other ARs the extra spread it adds is not offset by the recoil reduction. However with the AEK the positives are larger than the negatives. You should use it at all times if you want to use the AEK971, which means you cannot use a bipod or underslung weapon. If either of those are important pick any other AR.
The heavy barrel is the next go to for the AEK. It really brings spread under control and makes weapons much more aimable. The HB is the most popular attachment.
The flash suppressor is an ok choice if you are aiming to fire long bursts as it cuts down recoil.
Finally the laser sight. Many people prefer the PDW weapons because they have less recoil and spread so are more controllable from the hip. I find the higher damage and higher rate of fire sutis my play style better, not to mention the weapon can be used at range whereas a PDW is quite useless.
In conclusion, the best attachments are the heavy barrel and foregrip, along with the Kobra.