Just a couple scenarios that could seriously ruine your time in New Vegas

This Machine to all of them. Trail Carbine with scope if there's distance. One. Bullet. At. A. Time.
And when I see cazadors I think "not those again...".

Riot shotgun or SMGs usually work nicely against pretty buttlerflies for me (well, indirect fire from Mercy works best) but the other day I had my scoped hunting rifle on the hills east of Bonnie Springs. I had forgotten that the raiders there respawn as butterflies. I look through the scope, and I see this one cazador flitting from one side of the main drag's buidings to the other side really fast. I mean fast. He's moving. I thought what the hell, I was at about max draw distance, they had just popped onto the map, there's no way I can make this shot with a scoped rifle at a fast moving target from that range. POW! Down does pretty butterfly. I almost high fived myself. That was by far the best shot I'd ever made in this game. Like my sig says: One click: One kill.

-Gunny out.

If it was in the game, a MIRV for all scenarios.

For the Cazadors, you forgot to put "WHERE THE F*** DO YOU A******S KEEP COMING FROM!?!??!?!?"

Sniper rifle

All of them

I always have the Wild Wasteland trait so the Alien Blaster is usually my first solution to anything threatening. I don't waste it on things like Giant Mantises though.

I take the heroic route and hide behind Boone.