yeah, as those three majors seem to be exactly from USC, I shall elaborate for you.
Critical Studies is pretty much made fun of and looked down upon at USC. It's what you get into when you can't get into the harder programs. But it's perfectly lovely if you want to actually study films. But yes, you can take all these classes with the other majors.
Production is where the cool kids are at because it's what I was in =) But yeah, you take some crit studies and a mere 2 screenwriting courses. But Production is very technical. If you don't want to learn more than you'd ever need to know about sound, this is not for you. Production is not just for molding directors and producers -- but also Art Directors, Cinematographers, etc... In undergrad, they only accept 50 freshman and 50 transfers. Undergrad Production at USC is harder to get into than Yale Law School. It's one of the most selective programs in the country.
The Screenwriting Program is very intensive. You also take some Crit Studies and you take 2 classes where you actually make your own short films. But you take more classes in your major than the other majors because it's a BFA not a BA so it's harder to take any extra classes. Which means you really need to want to be a screenwriter or this program is hell. In undergrad, they only accept 25 students a year.
And btw, the key to getting into USC Film programs is grades, grades, grades! If you don't have good grades, don't bother. (Spielberg didn't get rejected twice because he wasn't talented, it's because he was a C student!)
-Your local USC expert
Fight on!
p.s. When I applied 6 years ago, I'm pretty sure they would only let me apply to one program, not all three. Maybe that has changed.