Public relations writing is a different ball game, but I find it to be so in a fun way. It is fast-paced and always changing. I also like that it is professional writing, but you still get some wiggle room to let your creativity out in your word and style choices.
My favorite area to focus on for marketing writing would have to be music publicity. I have not done much of that for a while now, but I enjoy helping my band friends get their stuff out there whenever the opportunity arises and get any documents together.