I prefer .pdf, and you can include a link to a free Adobe reader if you want with your email. But if your prospective employer can't open a .pdf you probably don't want them as an employer anyway.. consider it a screening tool.
But I get more irritated with Word files when I see all the squiggles below their names, and employers, and misspelled words, etc. Or if they have formatting characters turned on for some reason and I have to look at all those return arrows, or the worst is when they used some stupid font that I don't have, so I have to then pick an alternate? all those go in the trash.
The "rev control" that Christo points out is valid too... 1 vote for .pdf