Work. Earning more money is nice. The hours are better overall. At school, you had the hours of class and then a ton of hours outside of class doing homework, preparing for tests, and all the other associated time with that.
In general, work hours are more fixed and laid back. You have a set time in and out. When you get home, you can relax and not worry about anything hanging over your head. You have the money to live in a nicer place and get nicer things. If you're lucky, you feel like you have more of an effect on things.
In school, it never seemed like any of the knowledge was that useful or could be applied to anything. It was mostly theoretical and head in the clouds. It could be different for other fields, but it seems like most of what you learn is on-the-job training anyway. I personally don't use anything I learned in school anymore.
Of course, if your work sucks and you work 60+ hours/week, that's different.
The part that I will miss about school, though, is the environment where you can meet tons of different and diverse people. You can more easily find others with the same interests and you're closer to lots more people since you're probably living in the dorms with tons of others or in a greek place with a bunch of people too. At work, you might know a handful of coworkers who you actually socialize with and they may be a much different age so it's not as tightly knit.