If I was going to be doing a lot of photoshop work and wasn't looking for a laptop I would probably still go for a PC over a Mac. Allows a lot more flexibility in drive and hardware set up to get the most out of photoshop inn terms of scratch drives and fast hardware.
I'm very ill informed, I don't use photoshop so naturally assumed but it's all down to preference yet people still feel the need to argue which is better.

I'd use a pc anyways as I can't use the Mac os at all... I'm just too used to a windows os.