Mac, every time.

Been using them for years, even when a company I had box built PCs as a division, the company IT was mac, despite the abundance of cheap trade price parts for PCs.

Price? What's the cheapest car on the road and why don't we all drive it?

Backward compatibility? Only once, and in the latest Lion OSX, has the older non intel based software been ditched. Even then, you can dual boot with your old OSX if you must use very old software and won't upgrade it. Windows has had far more legacy moments.

Thinking on, probably spend far less than when PCs meant upgrading or crawling, although the rate of "speed" has slowed recently on both platforms. My recent iMac purchase of £1k was the first since my mac mini in 2004, which was £550. Not bad over 8 years