I would say it depends on what I'm doing. Photo editing then desktop no question. It used to be that my desktop was far superior as far as the hardware is concerned, but now that is not the case so all things being equal I'd have to tilt towards the laptop.
I prefer desktop instead of laptops. You can add more to them and customize them. Also, notebooks gets very hots if you have them on for more then one hour. So the palms start sweating which doesn't help when I type.
I tend to use my desktop mostly but just because it's all set up nice on my desk with a big screen... I only really use my laptop for checking email while I'm away and for powerpoint!