Helldivers 2

I am 100% a Quasar enjoyer, personally I like the cadence of it. You pull it out behind cover, let it spin up, shoulder-peek and delete something, then put it away for 10-15 seconds and it's ready to go all over again. No backpack slot, no ammo concerns, no reload animation, no waiting for a call-in to deal with a heavy. The Quasar projectile has no projectile drop either, making it hands-down the best weapon in the game to snipe bot dropships or distant objectives. I'd be reluctant to "waste" an EAT or RR shot on a Devastator, but the Quasar's infinite ammo means I'll happily zap one on that 15-second cadence if there's nothing bigger to shoot at.

One piece of advice for using the Quasar: don't use Aim-Down-Sights. I use ADS with most guns in this game, but not the Quasar. If you've only used it first-person then you might not realize that the third-person reticle for the Quasar gives way more information. The reticle spins and slowly turns from a square into a circle when it's about to fire, making it easier to time your shot when shoulder-peeking. The reticle turns red while it's on cooldown, white when it's good to go again. The ADS view gives you none of this information visually.

My group runs 8s if we feel like pushing ourselves, 7s if we want a less frantic pace. At those difficulties there are a lot of heavies to deal with, and the Quasar feels like the most flexible tool for dealing with them. The RR can shoot faster with a team reload, but that requires coordination that can be hard to manage under pressure. The EAT can give you two quick shots per call-in, but then you're left with a minute-long dry spell before the destroyer can give you any more rocket goodness.

The Autocannon will tend to struggle against Tanks and Hulks. That said, if you enjoy the AC then go with what you like! One of the regulars in my group usually brings an AC, and I'm happy to have them there because it can deal with other targets for which the Quasar isn't suited. Against bots the AC shreds walkers, against bugs it pops spewers, and against both its splash damage will clear chafe packs quickly. I wouldn't want a full team of ACs on a 7 or 8, but one or two are always welcome in the mix.