Which word processing program should you use? There's no real answer to that, of course -- it's what you prefer and what you're accustomed to.
Microsoft Word is my program of choice, but I have three computers that I use regularly for work and each one contains a different version of Word. One has Word 2003, another has Word 2000, and one (the dinosaur) even boasts Word 97. I've long thought I should update to Word 2010, but I'm familiar with the programs I have, can quickly find the features I need when I need them, and don't relish the idea of learning to navigate the newest version. I've seen Word 2010, as it came with a 60-day trial when I bought my notebook--they give you that taste for free, then when you're hooked they reel you in to make the sale. It looked like a unfamiliar landscape to me. So I stick with my old versions. For now.
The main problem with Word and its various versions is that if someone emails me a document in Word 2010, I can't read it if I'm on my older computers. The suffix is easily recognizable (.docx) and when I see that I know that when I open it I'll get something that looks like hieroglyphics.
Another popular program is Word Perfect, which I've used a couple of times and is also incompatible with my Word programs.
My solution to incompatibility issues is to ask (when I see. docx) that the document be sent to me in Rich Text Format. This is a terrific, universal program that's compatible with, as far as I know, all others. I've yet to be on a computer that couldn't open an RTF file. To find RTF, just open your document, go to File and choose Save As; then in Save As Type select Rich Text Format (suffix .rtf), and save your document. Voilą!
If you don't want the expense of buying MS Word or one of the other word processing programs, then you might want to take a look at Open Office Writer: www.openoffice.org. This is a free download and it has many of the same basic features that Word offers.
I'm telling you all this because as you get ready to send your work out--to publishers, editors, or even for contests--you might be asked to provide it in a certain format. It never hurts to know a few of the options.