Well, if Hibernate is causing you problems, I would go ahead and start another topic about how to fix it. Hibernate is extremely useful. It saves everything that is opened to the hard disk, and then resumes by loading it back up again. Its the equivelent of shutting down your computer.
Shutting down your computer is not hard on your computer at all. (Unless you press and hold the power button for 5 seconds, causing an instant shut down. You may loose data from doing this)
Sleep leaves your computer on, but puts it into a lower power mode. This makes it so that the computer can instantly start up again.
This turns the monitor, hard drive, and all devices inside the computer off, or into a low power state.
This is great for when switching in between classes, or when you are going to be leaving your computer for a certain period of time, but will be coming back to it soon.
No matter what option you choose, you should always save your data first, in case the worst happens and a program crashes, before powering down or powering off you computer.