Other important issues
Some considerations on the best computer for digital photography are basically the same as any Mac or PC decision.
The top issue for many buyers is cost. If you think the cheapest computer is the best computer for digital photography, go with a PC. The gap is closing, but Macs are still more expensive. On the other hand, Macs retain resale value better than PCs. Apple also somewhat makes up for the higher cost with customer service, security and native software.
Take a Mac laptop out of the box and even without an Internet connection, you can upload photos, shoot and manipulate photos with the built-in camera, make movies, learn guitar, play DVDs and play chess (you don't have the Internet, so you have nothing better to do).
Moreover, Apple customer service is renowned. Apple makes most of these native applications, so one call can handle questions about the machine, operating system and much of the software. The Mac geeks are even pretty good about troubleshooting other companies' software.
If you live near an Apple store, it has plenty of geeks on hand to answer any question. Online and phone support at Apple also is fairly useful.
Finally, in the Mac or PC security battle, Mac wins. The Mac operating system is less susceptible to viruses than Windows. The debate rages about the reason for the gap. Some attribute it to Apple's small market share, arguing it is not worth a hacker's time to attack a small percentage of computers. Others swear the operating system is simply more secure and no hacker has infiltrated its security walls.