Gimp is nice, but Photoshop is much better. Aside from the obvious fact it's free, the user face takes a little getting used to, but some of the general advantages I would say are 1) it's updated more often than PS. 2) Being open source, it's very customizable, and there are always new user-developed plugins & tweaks & twerks being released.
I personally use Photoshop with XP-Pen Artist 12 Pro drawing tablet with screen . It’s the best thing I ever did for photo editing. It’s seriously amazing.