Well, PS is overall the MUCH better programme. I have both installed on my machine, and I often jump between the two to get things done.
I've had problems with GIMP recognising my tablet, so PS is definitely superior in that sense.
GIMP is a wonderful programme, it does an amazing job with multi-layered items, and also with ease of use, but PS is ultimately more powerful.
Get both! It costs the same as buying PS alone 