I would have to say MS Word. It has always been Word from the first time I used it. I really haven't found a Word Processing program that I like more than MS Word, and since I just graduated college there hasn't really been any breaks in my life where I haven't needed a word processor. Even now that I am finished with school, until I decide to go for a Masters Degree, I find myself using it to write everything from to do list to HubPage drafts. Just in case your curious, I use excel the 2nd most and PowerPoint the 3rd. Power point is getting rather useless though since I have started using Prezzi, Captivate, and Camtasia.