I haven't used Gimp in perhaps a decade, but I can't imagine a worse UI than Adobe. At home, I have a free PDF reader, but at work (...when I was going to work...), I had to use Adobe's PDF editor. (Not that I edit the PDFs, I mostly just read them; occasionally a highlighter would be nice.) Ugly huge icons that I don't need and which take up lots of space. And next to nothing in the menu, except ways to turn on icon bars at the top and/or side, hopelessly emsmallening the page I actually want to read.
