---fudgesicle--- Adobe. Installs a ---steaming pile of meadow muffin--- load of files, takes for ever to load, and is very expensive. You pay that money only to have a new version come out each year and have to pay that money again.
I use pixelmator for Mac. It is contained to one single .app package, small file size, loads quick, and can do everything photoshop can do. Oh, and it's only $30. And you don't have to pay that $30 every damn year. You might also try gimp. It's free and for Mac/Linux/windows. Acorn for Mac is $30 too.