Must be the tenth time this has been asked.
There is no competition, photoshop is a much more powerfull package than gimp.
the possibilities that photoshop brings to the table put it miles ahead of gimp.
gimp is freeware, photoshop costs hudreds, even thousands of dollars, depending on the package you choose. its compatibility with other programmes from the adobe range and blablablabla.
there is no question that photoshop is the better package.
the only questions are, do you want to pay for legit photoshop or use freeware? and what youre requirments are of the package? if you learnt on gimp and only need the basic tools, then gimp is the one for you.
but if you learnt on photoshop, gimp just seems prehistoric.