There might be a spoiler or two in here:
First off, you must realize that there are no "correct" decisions to be made in the game. Think about what your mission was supposed to be, how it ended and then back to the times you were asked to make decisions.
Considering you were supposed to have left after making contact with the 33rd, every decision you make is wrong. Even if it seems like the positive choice, you shouldn't even be there making it.
"But no, you wanted to be the hero."
I think the "achievement" moniker is the problem because it makes you assume that you're getting a cookie for doing something awesome in the game, when that isn't the case. It's similar to the Manifest Destiny achievement in Red Dead Redemption that nets you 5 whole G for exterminating all of the buffalo in the game, effectively causing their extinction. Some achievement. The choice achievements in Spec Ops: The Line are simply there to show which path you took and are not to be seen as accomplishments.
In fact, if you look around you can find comments by the guy who wrote the game who claims that there is a 5th ending that supports the only correct decision the player can make: set the controller down and stop playing.
Everything else leads to horror and heartbreak.
God. Damn. What. A. Great. Fucking. Game.
I've seen the future. I can't afford it.