MACs freeze less. There is less lag. There are less viruses (by far). Graphics tend to be sharper and better. Those are just a few of the reasons.
Macs tend to be slower simply because they usually aren't compatible with the latest chipsets or processors. The apparent lag on PC's is only there due to all of the useless crap you have running on your computer. Reformat, defragment, or organize your work and it'll run just fine.
The reason PC's have more viruses is due to the fact that there are simply more PC's than there are Macs. It is more convenient to code a virus designed to infiltrate 80% (random statistic) of computers running windows rather than code another virus to infiltrate 15% of computers who run OSX. If the Mac user-base ever grows to the size of the PC user base, i'm quite sure that they'll get an equivalent amount of viruses since both OS's are equally vulnerable to viruses.
Graphics are sharper on Mac's? Since when? When was the last time you've bought a new Nvidia or ATI graphics card that supported Macs straight out of the box? PCs receive the cream of the crop, in terms of graphics cards, months before Macs are supported. If you're referring to Adobe Photoshop CS4 etc. those programs just as efficiently on Macs as they do PCs.
Granted Macs OS's are better for laptops since they're less vulnerable to viruses at the moment, PCs still dominate the market and for good reason. They're cheaper, more customizable (internally), & support a wider array of programs. The final decision is still up to you on whether to get a Mac or a PC, but i recommended getting whichever one better fulfills your needs.