a) Use RTF files, because it is in fact the Lowest Common Denominator, and everyone will be able to open it, no matter what platform or software they are using. Seriously. Its like a text file, except with bold, and Italic.
b) Use ODT files, because it is an open standard that everybody but Microsoft supports, and it lets people know that I'm one of the 3lites that doesn't submit to the will of Microsoft
c) Send a Microsoft works document because.... welll... because it came with the computer for free, and I don't know how to save it as anything else, and it never occurred to me that someone might not be able to open a works document.
d) Send a word doc, because it is the lowest common denominator MS standard, and everybody will be able to open it, even if they are 3lites who use Openoffice, or some other non Microsoft program.
e) Send a word Docx or docm file, because I like forcing Microsoft customers to upgrade their shit, install useless upgrades, and otherwise be a pain in the ass to people running legacy MS software, or non Microsoft programs.
f) Send a wps file of your cover letter, and a doc file of your resume... because... you know... I want to make sure people know I don't adhere to any standards or logic, whatsoever.
g)Send a PDF file. Because.... ??? I really like it when people can modify and change my shit. Or load it into an ebook reader.
If you choose anything besides A, or D, I will probably not hire you, use you as an intern, or read your manuscript. I'm just saying. This is just me. I'm sure there are people who would hold D against you, out there in the world. But seriously. You can NEVER, EVER go wrong with A. Ever.