I've been using both platforms for years, and recently purchased in iMac for home. I am a graphic designer, and the choice was obvious. Graphics are amazing, and computer is quick and bug-free. The sims 3 also runs like a dream, with no crashes and no lag.
However, if you are a big gamer, it is often harder to find the games you want for mac, and many custom programs available at mod the sims are for pc only.
That being said, I love my iMac so much that I wouldn't trade it for the world.
Yeah, go MAC! I disagree with the "image" comment as well. My new Mac is about twice as fast and powerful than my dell. Macs have come a long way and not only offer the "image", but offer the most current and fastest processing power and speed. Go for it!