There is no debate here. MacBook Pro. Hands down.
Firstly, in regards to Windows based OS laptops, Dell is at the bottom of the list. The internal hardware is CHEAP.
I am not giving you a biased opinion because I love my MacBook Pro. I'm giving you my honest opinion because my MacBook Pro was bought one to two weeks ago, but for 3-4 years before I saw the light, I was working with a Dell XPS (which is now in the garbage, may I add.)
Backing up to why Dells are crap... all comes down to the cheap hardware. The Dell XPS is marketed as being a "gaming laptop." This should mean that if it runs hard, the laptop should be able to keep itself in check. Wrong. I had severe overheating issues from day one with my Dell XPS. Again, it came down to cheap internal parts. The fan was flimsy plastic, and never ran well enough to keep the XPS cool. No laptop should be dead in a mere 3 years. I had to send the XPS in for repairs on more than one occasion due to heat. I payed extra to keep having the fan replaced and fixed. The cheap parts, were just "repaired" with more cheap parts, and the heat won. Internal hardware fried and that was the end of the XPS. Also, in regards to it being a "gaming" laptop, it was crap! It could barely even handle simple FaceBook games. It would lag, and get so sluggish.
Just do a simple Google search about the Dell XPS and severe heat issues. You're going to get dozens and dozens of links coming up. There are no exceptions, this is what will happen to your XPS.
If you're worried about viruses on a Mac, don't be. The majority of PC users, use Windows based computers. The majority of all malware, viruses, and other things out there, are geared towards Windows, not the Mac OS. If you use the Mac smartly and obviously don't click stupid things, you can use it without ever seeing one virus pop up on your machine. Macs dont even NEED antivirus protection the way a Windows based PC does.
I use Windows 7 at work, and Snow Leopard at home. I have to say I prefer Snow Leopard above Windows 7. Simplicity is AMAZING. Especially if you do photo editing, and video editing, you're going to love all the fun programs that come standard on the MacBook Pro. As for using the Mac for school, you're going to have to shell out an additional $120 or so for the Microsoft Office programs (Word, excel, powerpoint, etc), these do not come standard on the Mac.
I would never ever go back to a Dell or any other Windows based PC for that matter. No way.