Great to have a new fragrance junkie on board! I think your first 3 choices are pretty solid and should do well for a variety of situations. The Dreamer is a great going-out scent- you'll certainly stand out from all the Acqua di Gios and Abercrombie Fierce that usually fill the air in a college town. YSL PH is a pretty strong fragrance, and you may find it challenging to wear. I think It'd go great when you really need to make an impression, but please go easy on your trigger-finger! The Nautica is a pretty decent everyday scent for class work and the like, but I'm sure you had that figured out seeing as how you didn't really ask for advice on it
It's always fun to have to take the time and decide what to wear. Don't be afraid to mix it up every once in a while- after all, your mood is the best judge on what you should wear. Enjoy!