One problem is that asking whether PC's or Macs are better is like asking whether being Catholic is better than being Protestant. Everyone believes in what they grew up with and are used to. ;-)
I'm a little different, because I use both PC's and Macs. So, how to decide? First, ask yourself some questions. Number one is whether there is a preference at your college or in your department. Some colleges will support one platform much more than the other. If that's the case, I would go with whatever is the dominant platform. If you have a problem or a question, it's just easier to get help that way. And some colleges actually have a requirement one way or the other. At a certain highly competitive private college in Pennsylvania, for example, Chemistry majors are required to have PC's, but Physics majors are required to have Macs. And no, I do not know what dual majors do about that. But find out if there is a preference where you will be. If so, go with the flow.
Other than that, make sure you are comparing comparable models. ( I was about to say "comparing apples to apples," but that's a little too cute.) The big argument in favor of PC's is that they are available cheaply. But a $300 PC is a piece of junk. Top line PC's cost just about the same money as Macs. Macs don't have a low-end version. So that argument is *partly* bogus. Partly, but not completely. It may make sense to get a cheap PC and use it just for a couple of years while you are in college. That's especially true if you are already a junior or something. If you are going to be a new first year student in the fall, then you want your computer to last a full four years, and you should by a good quality product, regardless of whether it is a PC or a Mac.
The other major argument is that there is more software for the PC than for the Mac. That argument is now 100 percent bogus, because Macs run BOTH the Mac OS and Windows 7. You can therefore run PC-only software, Mac-only software, or both Mac and PC software. You have many more options with a Mac than with a PC. This is the complete opposite of what was true 5 years ago.
If you buy a Mac, however, it makes sense to emphasize using the Mac side, especially for any online work. There are no viruses -- ZERO -- that have ever been found "in the wild" for Macs. You may have read that people have demonstrated the possibility of Mac viruses in the lab. That's true, and it is something to keep in mind. But no Mac user that I know of bothers one whit about things like anti-virus programs. They just aren't necessary yet, and probably won't be necessary for many years, if ever. On the other hand, I am absolutely religious about keeping my PC anti-virus software up to date. It's a pain in the a--, but it is vital. There are thousands of PC viruses out there, and more every week. Never, never go online for any purpose with a PC unless you are sure you have the latest updates to your anti-virus program.
If it sounds like I am leaning toward the Mac for you, I am, but it is more a matter of how careful you are going to be about keeping your computer protected, and whether you can make do with a low priced computer. If you can get by with something cheap AND your are very vigilant, then a PC makes more sense. If you just want to use the the thing and not worry about it, then go with a Mac.
Good luck, and I hope this helps.