It's sort of both. When I first started doing digital painting, I had a laptop that just didn't run Photoshop or Adobe very well- it simply didn't have the processing power. I found that GIMP and Mypaint worked just fine on it, though. Now that I have a much more powerful computer, I have gotten used to Mypaint and GIMP and actually prefer a lot of the features they offer. I also love the idea of open-source software and the communities that form around them, improving them and making them more powerful and flexible. I will probably start doing more in PS if only because the industry expects a certain familiarity with it, but the brush dynamics leave something to be desired IMO.