Before we get started a tip for you:
Generally, the best builds in this game use one weapon dedicated to a single target and the other to crowd control.
As for the rest of the gear: Use whatever can complement your weakness so that you would have an all-around great build rather than a one-trick pony. This is so you would have an option for every situation and wouldn't get killed because you dedicated all your arsenal to one specific thing.

I use pretty much the same pickaxe, equipment, and armor upgrades for all builds I have.

*This is the same for all classes

*This is the same for all my Enginner builds

*This is the same for all my Enginner builds

I often change my throwables depending on a mission type, the builds of my teammates, and many many more variables so that's why I will not go over them in my builds. But in case the build heavily benefits from a particular throwable type I will give it a mention.

*This is the same for all classes

This build uses Warhog with Pump Action for single-target elimination and Breach Cutter with Spinning Death for dealing with groups of smaller enemies.

I recommend using L.U.R.E. as your throwable as with them you can make enemies walk into your Spinning Death plasma nodes.

• Resupplier
  
• Born Ready
  
• Vampire
  
• Dash
  
• Iron Will

This build was made for Elimination missions but is also good for other mission types.

Use your Neuro-Lasso to slow down Dreadnought while you wait for just the right moment to strike with a well-placed Hyper Propellant shot and deal massive amounts of damage to the boss.
And if you are planning on using this build for other mission types you can use your Lok-1 to help deal with smaller enemies and use PGL to disintegrate anything with a sizable heath bar.

• Resupplier
  
• Born Ready
  
• Elemental Insulation
  
• Dash
  
• Iron Will

This build is all-around great no matter what you put it through.
Executioner is one of if not the best LOK-1 overclocks and a great source of single-target damage.
And Volatile Impact Reactor is just as good for dealing with crowds.

• Resupplier
  
• Born Ready
  
• Vampire
  
• Dash
  
• Iron Will

*Weapon paintjobs were applied with the help of No Cosmetic Restrictions mod

This is as straightforward as it gets.
Use the shotgun for single targets, and the grenade launcher for crowds of weaker enemies.

Your warthog is more than capable of engaging in long distances so don't be afraid to kill those pesky Web Spitters up there on the ceiling.
As for PGL - it can set the whole swarm on fire with one well-placed shot.
I almost never use clean overclocks because I think they are boring but MAN, setting like a trillion bugs with Clean Sweep doesn't get old.

Oh and btw, with PGL, try to shoot the swarm at the center and from above to get the most value out of the huge area of effect.

• Resupplier
  
• Born Ready
  
• Vampire
  
• Dash
  
• Iron Will

This build has Explosive Chemical Rounds for swarms and Light-Weight Cases for everything and anything with more legs than two.

Explosive Chemical Rounds has great ammo economy since all you have to do is fire each time you have 3 locks on the enemy in the center of the pack and all nearby enemies will take damage from the explosion and possibly get feared because of it. A straight-up BANGER.

Breach Cutter is objectively Engie's strongest secondary and Light-Weight Cases is just an all-around great option. It's a small bonus that goes a long way.
All this Overclock does is let you use the Breach Cutter for a bit more (with +3 to ammo) and more often (with -0.2s to reload time).

• Resupplier
  
• Born Ready
  
• Vampire
  
• Dash
  
• Iron Will

This is a fun build that uses Stubby with Hyperalloy Assembly Overclock for close to medium-range engagements and Shard Diffractor with Overdrive Booster for anything outside of the range of Stubby.

Hyperalloy Assembly turns what (at least to me) felt like an underperforming weapon and turns it into a good source of single-target damage with a high fire rate.
And Overdrive Booster is just a big laser with potentially high single-target damage.

I'd admit that this isn't the most balanced build and is a bit of an overkill but it isn't that big of a deal in a team setting as you can cover the weaknesses of each other's builds.

• Resupplier
  
• Born Ready
  
• Vampire
  
• Dash
  
• Iron Will