Against foes who are armored, use a slow firing, heavy hitting gun (Or melee weapon), preferably with Armor Piercing ammo (Any type that reduces their DT.). Ignore the DPS against armored monsters. 10mm SMG has an INSANELY high DPS, but will BARELY hurt an armored foe, because they can easily absorb most of the damage from each of those rapid fire shots. It's the same reason why shotguns do next to nothing against armored targets (Sure, that shotty might be hitting for 77 DPS, at 7.7 damage per round of buckshot, but that DT of 10 on that Deathclaw means it absorbs the full 7.7 damage from EACH round of buckshot, meaning he's only being tickled by that shotty.). A Sniper Rifle in good condition with AP rounds will rip through Cazadors, providing you can actually hit them. If they get in close, I'd suggest going for the wings. The wings are fairly easy to target, and will knock them to the ground, making them a VERY easy kill for your next shot or two.
When I first encountered cazadors, I got raped. Then the second time I encountered them, raped again. After that, I avoided them as best I could, until I decided to try sniping from a distance with said sniper rifle, and preferably from cover of stealth for the added crit.
When I first encountered cazadors, I got raped. Then the second time I encountered them, raped again. After that, I avoided them as best I could, until I decided to try sniping from a distance with said sniper rifle, and preferably from cover of stealth for the added crit.