Edit 1: I added more info about what you can do between "waves" and what weapons I took.
I got the achievement playing alone, so I'll add the weapons that I used and at what moment
(I can't help you with what generator I destroyed first because I forgot it, but the last generator was the right generator (not the generator near the entrance))
First wave: Destroy almost every pod, except the ones on every 2nd floor. It's easy to fight with juvies now than later. I had the Hammerburst before the Swarmak, and I picked the Boomshot that is near the left generator (near the entrance) (1st floor). Put 2 grenades tags not so far so you can hear when they exploded and get ready if some juvies are near you
I was standing on the first floor of the right generator (not the generator near the entrance) After I popped the first blister with Hammerburst, I switched it for the Boomshot. I never changed the Lancer because I forgot to clean every pod and on 3rd wave I fought with 5 juvies, and Lancer helped me to destroy the generators very easy
Second wave: I didn't have much trouble with this, I picked the Mulcher near the infinite ammo. I was on the same spot that before. If you have grenades, tag them like on first wave
Third wave: After the checkpoint, change whatever weapon you have for the torque on the left, (Don't change Lancer), if you still have grenades, tag them. After that, run as fast as you can to the left generator (near the entrance) (2nd floor). Now change the Lancer for the Boomshot near the ammo box. Fire at will at the Scion Mulchers. If you get active reload and a little of luck, you have killed the 2 Scion with the Boomshot, then took again the Lancer. If you didn't killed the Scions, do it ASAP. This is risky, but it's one of the best places to stay to destroy the blister near the tail with the Snub. After you destroyed the blister, remember to run near the generator so the missiles don't kill you. You can try to get the Torque Bow's arrow to the knee from here, and if you run out of ammo, you can go to the far right genertator to get more ammo for the Torque Bow. If you were asking why I didn't destroy the pods from the 2nd floor, is because 75% of the time a Swarm can climb the stairs and he appears near you, and if you have the pods, they try to cover and then shoot you (or Marcus), this is a real life guard (Mostly of the time if you don't have the pods the Swarm runs to kill you with melee, or he can DBNO Marcus).
(Maybe you can try Gnasher over Snub because you are very close from the blister, but I never tried it) (I tried with the Longshot, but it was very difficult)
Fourth wave: My final generator was the right generator (not the generator near the entrance), so I destroyed it, and I went to the second floor to get the Markza, and I picked the back blister because it's more easy IMO. I didn't have so much trouble like on third wave.
Markza (back blister, not the chin blister)
Good luck everyone
(Sorry for my english)