Only go as big as you need.
Do you know what style/brand of door you want?
This is the door I went with 12x14 they have a 20R rating they are injected foam with full view windows
http://www.chiohd.com/docs/default-source/default-document-library/garage-doors-with-a-door-flyer-3285.pdf?sfvrsn=0
12x12 gets my vote