Choosing between MS Word, PDF, and latex formats when submitting a manuscript for publication when all are allowed?
That all depends on the journal you're submitting to. Quite some journals that accept Latex, also provide a template to use. With a template available and knowledge of Latex, it should be fairly easy to convert the GoogleDoc to Latex if you download as HTML and then use eg Pandoc to convert to Latex (explained here). 

But people who are not comfortable with Latex, are likely better of using another option. Converting from GoogleDocs to .doc or .docx generally also requires an in-between step using PDF, and will generally give some layout issues, but when a paper is bound to be submitted it's not really the time to learn Latex.