Okay, so I think this may be applicable to the "Hector Wrecker" achievement. The best spots I found Hector's to inhabit were 1-4 (Ditchslap), 2-5 (The Cube), and 3-5 (Big Trouble).
The first time you encounter a Hector is in the first mission. For those of you who are new to this game you defeat Hectors by, as if it wasn't obvious enough, shooting the red section on its chest.
On 1-4, in Normal difficulty, right out of the gate, there are three Hectors. Either have powerful or Pesticide weapon, as I found the Mech's that are air-dropped in don't help very much except for taking out the ants and spiders.
A bit later on in 2-5, when Ops is getting a ship to retrieve the VIP's (after you self-destruct the first dropship) there will be four Hectors to contend with, along with a few insects.
Your best bet, however, will be 3-5. On Normal difficulty, you can't fight a SINGLE horde of Ravagers without coming across one, it feels like.
Just as a side note, you should be able to get this on your first playthrough. There are a few randomly strewn about, though.