I'm with Loxaris, that I haven't used Krita (I think I downloaded it once, but couldn't get it to work), but use mainly Gimp. I'm using Gimp for work at a game startup. Gimp has a lot of things you can customize, and I've customized mine to suit my needs.  

It has a bit of a learning curve after using photoshop so long, but for me, it works pretty well for drawing too (I have Intuos4). I'm missing Photoshop's adjustment layers, but I like it how I can customize the tools to work how I want them to. And what EmiXNaru said abou there not being brushes - you can download and make brushes in Gimp too.

I also like it that Gimp can open and save images in .psd, though it won't understand folders. Even so, it makes things easier when I have other artists in the team that use photoshop.

A downside to a new user is that tweaking things to the way you like will take some time, before you get everything optimized for you.

I'm not sure what you're going to do with a free drawing program, but another free option could be MyPaint. It works like a dream for people who like to draw, and it has beautiful brushes. I've also installed it in a usb stick, so it's not too heavy either. The only two minuses I can think of are not being able to determine a size for a canvas (it has infinite canvas!), and no editing stuff (like cut and paste, color adjustment...), but they're work-aroundable. Sometimes I start a drawing in MyPaint and finish it in Gimp.