ABSOLUTELY NECESSARY TIER DLC:
Gage mod pack. The pack grants a lot of excellent scopes and compensators which are extremely useful, because otherwise you would have to find them randomly. It pays off mote the longer you play, so if you don't see yourself playing this game for that long it might not be worth it.
High Tier:
Gage pack #1. It adds grenades, firing mods, and grips, which are all super useful, but the guns themselves are kinda sub par. The eagle is okay, pistol is okay, and I don't even remember the third gun.
Gage Sniper Pack: adds the most powerful weapons in the game, sniper rifles. While people say that they're absurdly overpowered, I would argue the low ROF and inability to clear crowds balances em out. These guns will turn shields into just ordinary cannon fodder, just for that it's really fantastic.
Gage Assault pack: Really powerful all rounders In this pack, FAMAS is God tier, GL40 Is fun, everything else is good.
Mid tier:
Gage Shotgun pack: It's okay. Doesn't add anything too amazing, the HE rounds are sorta useful I guess.
Gage Pack #2: LMGS are okay I guess. I'm not a big fan but eh.
Improved WHY tier: Armored transport and soundtracks. Soundtracks are good but not necessary, armored transport is suffering.
As for the heist dlcs, get em if you wanna play the heists solo. Armored transport has okay weapons, HM has the best weapons.