What is the best Word format to save to?

Help.

I have been using my Macbook Pro for about 5 years in an office setting, where everyone else in our business uses PC.

I use Parallels and run Windows 7.

However, I write almost every document in Pages, Version 5.1, and I run OS X Version 10.9.2

My problem is that I export my Pages document to Word, then I drag it over to Parallels Desktop and open it in Word to clean up any alignment and formattting issues.

There are two options in Pages, save to Word .doc (Word 1997-2004 compatible) or docx

Almost always when I email the Word document, the recepient complains that the formatting is off in some way.

Can anyone offer any advice?

Is one format better than the other, in terms of .doc or .docx, and/or is there something else I need to alter as I save the document to Word?

Thanks,

Dan