This is some strategic loadout ideas for the Engineer. It is based largely on opinion, and these suggestions may or may not fit your play style or level. Please do not change the existing loadouts, except to fix grammar or spelling. Instead add a new loadout to the article.
Default Loadout
The weapons that are pre-bought when you start playing the game.
Primary: M4A4 -This is a balanced AR, meaning that it is designed to be about average in all of its stats.
Secondary: USP -A single-fire handgun that has slightly below average performance.
Long Range Loadout
This is about as long range as the engineer gets!
Primary: ARX 160 -This single-fire AR has good accuracy, damage and capacity, but lacks ROF.
Secondary: Katana -If the enemy gets to close, chop his head off. But remember to click ON your opponent.
Attachment: Heartbeat Sensor -This way you know where your enemy is before he can see you.
Skill: Iron Grip -Increases accuracy.
Killstreak: Battle Turret, or Rocket Sentry - Better at long range than the Drone or Tesla Coil. With your Efficiency skill and a good trigger finger, you should be able to place a few of these in a single match.
Long-Range Support
This class is all about sustained RoF and range.
Primary: QBZ 95 -A good AR, with evenly spread stats.
Secondary: MP9 -As close as a secondary can get to an AR. when out of ammo in a fight, switch to this.
Attachment: Extended Mags -Extra ammo.
Skill: Iron Grip -With this, you can focus on shooting, without worrying about crouching.
Killstreak: Combat Drone -Shoots for you!
CQC
You have to kill your enemies as fast as possible, or they kill you!
Primary: Scar Assault Rifle: -It's powerful, RoF is good, and it's powerful.
Secondary: Katana: -Comes in handy up close, but it takes getting used to. Also reflects projectiles.
Attachment: Laser Sight: -Pretty much makes the gun more powerful.
Skill: Adrenaline: -The increase in RoF this gives is terrific.
Killstreak: Tesla Coil: This works well, because you don't have to wait for it to aim.
Solo Loadout
Is built around the idea of being away from your team as long as possible without any help. Places priority on using your own weapons to kill for you
Primary: QBZ 95 - A good, all around, evenly balanced gun. Does exceptional damage for a slightly lower ROF
Secondary: First Blood- A good melee weapon, but is best used as a last resort weapon. Out damages the Katana, but only if it has a perk with an increased fire rate or critical chance
Attachment: Laser Sight- places emphasis on being able to eliminate opponents quickly and efficiently. Accuracy is key
Skill: Repair Bots- An amazing ability that allows you to quickly recover from fights, as well as being able to leave healthpacks for your team
Killstreak: Any- As the loadout revolves around the SFH1 commando playstyle, killstreaks aren't as important here as they are for other loadouts.
Hyper Offensive
The aim is maximizing damage output. Works best for solo, but is suitable for anything.
Primary: QBZ 95 / M4A4 - The engineer's best full auto primaries. Which one you should pick depends on which of yours has a better dps (damage * rate of fire). If the dps is about equal, give priority to secondary effects then to ammo capacity then to accuracy.
Secondary: Katana - Get good with switching between your primary and secondary. The katana does huge damage, and getting in close quarters with this is your only chance against snipers. Bonus points for reflecting rockets (the slower, seeking ones are a lot easier than the rpg).
Attachment: Loudener - This can give you up to +25% damage against everything. Engineers aren't crit/ headshot oriented like snipers or generals, so this is easily the best attachment. The loss in range is a price worth paying.
Skill: Adrenaline - Essential against other automatic weapon users, and in more crowded maps. You get the bonus during acid/fire damage which is a cool bonus.
Killstreak: Combat Drone / Tesla Coil - The engineer doesn't have any particularly good killstreaks but these are the best two. Use combat bots in bigger maps, and the tesla coil in smaller ones and during capture the flag.