Personally, I will always choose PC...
I will also choose AMD...
I like my things to last a long time. My current PC is well into its 5th year, and its still going strong. I can add RAM, change CPU, upgrade HDD, install new DVD drives... so that my PC will serve my needs many years into its life.
It's setup as follows:
CPU: Athlon XP 2400+
M/B: Gigabyte GA-7VRXP
RAM: DDR333 1GB
HDD: 2x 80GB 7200RPM RAID0
Video: nVidia GeForce2 MX400
It's currently a bit slow when I open those 20-30MB PS files, but then I don't do it so often because I'm not pro. Unless you're constantly opening and closing these files, it's not that crucial to have a Super Computer on your desktop. You just need something workable. I find that there is too much hype over the CPU speed. 2 Core, 4 Core... well they help, but only so much. Your system will only run as fast as the weakest link... and that's usually the HDD. Hence, RAID0, RAID0+1 or RAID5 would really help. Having enough RAM is also important else the the system will scribe onto the HDD (which is the weakest link).
If you set up your PC properly, it will run efficiently. My home PC is faster than my office PC, even though my office PC is much newer.
With a MAC... you can only sit around and wait for it to become unusable... Also, I can't stand MAC advertisements. They mix truth with falsehood, like the devils do... and their machines are mostly only so-so. They are just different... not necessarily better. We can go into the details and compare point for point... but there's really no point in doing that. Just pick the machine you are comfortable with
I like AMD because it is cheaper, and its upgrade path is better. They tend to stick to the same socket for longer time (except for socket 939). This means I can buy a faster CPU later on. AMD is also a more open company who is willing to work with others for better chipsets.
My PC is a bit slow now... I think I should upgrade in 3Q or later when the price drops. I'm quite looking forward to it.