PDFs can be zoomed to fit the width. So don't worry about sizes. Just make sure all the pages and side margins are congruent. Here's why: On my iPod touch I've been using GoodReader for about two years now. It has this very useful horizontal lock feature that once you reach the zoom level you want, you tap that button and you can only scroll vertically. I'm reading PDFs by holding it sideways (bottom button):
http://k.min.us/ic9dcE.png
And it's incredibly annoying when an author doesn't use the same margin width for each page because I have to mess around with the zoom, go back and forth... Anyway. Congruency.
Word 2010 with Adobe Acrobat X, though not perfect, is probably the pinnacle of PDF creation. But no matter the software you choose, always keep the original .odt, .doc, .docx or .rtf, just in case. You never know when you're gonna need them or what format will come out 5 years from now.

And it will make converting them so much more easier.