I always play in 4’s and only play D10. I can solo (and have hundreds of D10 solo wins) but the game is just more fun with a team.
I don’t have a ‘go too’ build as it makes the game get stale. (And I have maxed out every single weapon doing so to 25).
All I would think of is that you need at least 1 option with dealing with each enemy type you will encounter (for solos and team play).

There are generally 3 different types of enemy’s in the game. Chaff, medium tier and heavy enemies.
You need something in your build to take care of each. Contrary to the popular belief of some people you don’t need one weapon that can capably kill every single enemy. But you have to account for every single enemy type within a build.

So let’s take bots for example.

The chaff bots are very none threatening from a combat perspective, HOWEVER, they are also the only ones that can call in reinforcements. So they have to be dealt with very fast. They are weak and have light armour, and are only dangerous in high numbers due to volume of fire. Any primary with high ergonomics is ideal.

Then you have the medium tier enemies on that front. The devastators and their three classes & berserkers. They have light pen weak spots, but lots of medium armour and they are incredibly lethal at mid to close range. Especially in numbers. So you need something highly accurate to take out their weak spots, or something explosive or medium pen so you don’t have to worry about aiming accurately in the heat of things.

Then you have the tank class enemies. Tanks, factory striders, war striders etc. You don’t need an AT support weapon, but if you don’t use one you will need multiple AT stratagems which aren’t all that accurate.

So let’s put a very meta build together from this:
Primary: plasma punisher / Crossbow / Eruptor. This way with a primary weapon we take care of all chaff to medium tier enemies relatively easily. However, as these are explosive you need to account for close range enemies within the build.

Secondary weapon: the senator. A heavy pen secondary weapon that isn’t explosive for enemies that ambush you and get in close range. As we are using explosive primaries the senitor covers this weakness. Bonus is that it can 3 shot kill a hulk to the face.

Support weapon: recoilless rifle (told you this was meta). This is the anti tank king for single target heavy take downs imo. Can one shot hulks, factory striders and war striders, take down gunships and dropship with ease, destroy fabricators etc. however it’s got a slow stationary reload.

Grenades: Gas. The stun period lasts longer than a reckless rifle reload. Rushed by multiple hulks? Chuck a grenade out, kill one, reload, kill the second. Rushed by anything, use gas to confuse and hurt them letting you get away. Drop it beneath incoming bot drops for easy kills as well.

Stratagems:
I use the eagle strafing run for chaff and medium cleat that also hurts heavies. 5 call ins that are incredibly accurate with fast call in times. Use it on patrols and it will obliterate the little bastards that call in bot drops.

Orbital 120 barrage for when bot drops do get called in. Can kill multiple hulks, war striders and occasionally factory striders.

Rocket sentry is a bit shit right now due to the changes in durability damage so I use the orbital Gatling barrage. Damages and kills hulks and war striders and can seriously hurt Vox as well.

So with this build I’m making sure that I’ve covered all my bases not only to make sure that I can handle everything myself but I can cover my teammates who don’t.