Battlefield 4 is one of the few online games that still relies on classes for its loadouts, and as such crafting an ideal loadout becomes even more important. You absolutely have to craft your loadout with your class' strengths and weaknesses in mind if you want to dominate online. With that said, here are our favorite loadouts for each of the classes in the game.

Engineer

Primary: AK 5C w/Holo 1x Scope, Tactical Light, Angled Grip or Folding Grip, No Barrel Attachment

Secondary: P226 w/Ghost Ring, Laser Sight, and Flash Hider

Gadget One: RPG-7V2 for anti-vehicle combat, or RIM-92 Stinger for anti-air combat

Gadget Two: M2 Slam for an aggressive build, or the Repair Tool for support builds

Grenades: V40 Mini

Field Upgrades: Anti-Tank for aggressive builds, or Mechanic for support builds

Everybody knows the Engineer is deadly against vehicles, but in order to be truly competitive it has to be able to take down infantry enemies just as easily. This build focuses on the Engineer's two strong points: ground-based infantry combat, and vehicle-based combat. An Engineer with an RPG-7V2, M2 Slams, and the Anti-Tank Field Upgrade equipped is practically unstoppable against light and heavy tanks, as well as troop transport vehicles. Remember to drop your Slams each time you spawn, as they'll remain on the battlefield when you die up to a certain limit. 

The powerful AK 5C is the best Carbine in the game, and also one of the earliest you can unlock. It can easily carry you from level 1 to 25. Adding stabilizing attachments like the Folding Grip makes it powerful at both close and mid range.

If you aim to help your vehicles rather than hinder enemy vehicles, go with a Repair Tool and keep the combat to a minimum, and in close ranges. Try to stay with your vehicle most of the time.

Assault

Primary: ACE 23 w/Coyote [RDS], Muzzle Brake, Angled Grip or Folding Grip

Secondary: P226 w/Ghost Ring, Laser Sight, and Flash Hider

Gadget One: Defibrillator

Gadget Two: Medic Bag

Grenades: RGO Impact

Field Upgrades: Offensive

This build focuses on keeping the Assault class offensive, with a Field Upgrade that keeps making the Assault stronger and more durable, and a primary weapon that's just about unmatched when it comes purely down to emptying bullets into a target precisely. Use only Grips that increase your stability, never ones that increase it at the cost of another stat. 

With Assault, you want to be at the forefront of the battlefield. This will enable you to come across allied soldiers who are wounded and need help from a Medic Bag, or worse, a Defibrillator. Always use either when you see the need for it; it's the best way to earn more points as you run around on the battlefield.

Recon

Primary: SRR-61 w/Ballistic [40x] for long-range combat or JGM-4 [4x] for standard sniping, Range Finder, Suppressor for stealthy play or Flash Hider for aggressive play, and Bipod

Secondary: P226 w/Ghost Ring, Laser Sight and Flash Hider

Gadget One: PLO

Gadget Two: C4 Explosive

Grenade: V40 Mini

Field Upgrades: Sniper for aggressive play, or Spec Ops for sneaky play

Snipers can be aggressive or stealthy. An aggressive sniper must always be on the move, lest someone see your muzzle flash and come up behind you. Use C4 to mitigate this risk when you find a truly excellent sniping spot. Instead of standing on a hillside like most snipers seem to do in the game, find a good bush to hide in or a collapsed building to lie under. In these locations, it can be harder to make out your character model from the environment textures. Failing this, just hide in a dark corner.

Support

Primary: QBB-951 for spray and pray, or AK 5C for accurate play, w/HD-33 [1x] scope, Tactical Light, Compensator, and Bipod (for QBB-951)/Folding Grip (AK 5C)

Secondary: P226 w/Ghost Ring, Laser Sight, and Flash Hider

Gadget One: Ammo Box for Support play, or XM25 Airburst for aggressive anti-infantry play

Gadget Two: M224 Mortar or UCAV

Grenades: V40 Mini

Field Upgrades: Indirect Fire 

The Support class is one of the most flexible in the game, as it can be used as either an anti-vehicle class or as a, well, support class to aid its fellow soldiers. When using Support to help out your allies, you'll want to drop an Ammo Box around a contested Rush or Conquest location to help out your buddies. Don't even bother with the weaker Ammo Bag, which only resupplies one soldier. You can also lay down a lot of suppressing fire with the QBB-951, which is the best of the Support LMGs. On the other hand, it's not very accurate, and likely to give away your position. If you're serious about inantry combat, you'll want to go with the AK 5C Carbine.

The Support's anti-vehicle and infantry tactics are numerous, and revolve largely around the use of the Mortar and the UCAV guided drone plane. Hit a soldier with either of these, and they're dead. Drop one on a damaged vehicle, and you'll score multiple kills and a Vehicle Destroyed bonus.