I would recommend a high end PC as the software base is just a lot broader. I used to have Mac but eventually switched to PC because of this.
PC's are also a lot cheaper for the same processing power. Just install plenty of RAM for your Photoshop and it'll be great.
I'd also recommend using an SSD (Solid State Disk) as our OS disk, they are lightning fast.
I've recently installed Windows 7 on an OCZ Vertex2 SSD disk. Best thing I ever did. Word and Excel opens in 0.5 second - yes literally, from double clicking the icon to being ready to type. The splash screen only shows as a quick flash
It's a joy to use.