Then you've got a problem.
Usually I tend to pick up Dragon instead of Dungeon if I can only get the one. As a game wears on, I usually end up writing more of my own adventures and Dungeon becomes less useful. But even at uni I tended to play with a small, cohesive group, and having the added extras to throw into my game was more important than having an adventure laying around.
If you plan on running a campaing, then Dragon would probably just edge through with my vote.
On the other hand, if you're groups not cohesive and you're just looking for a quick game every week or two, or if you think college is going to suck up a great deal of your free time that would once be spent writing adventures, Dungeon wins out.
Me, personally, I'd stick with Dragon.