Which of these document types is the most ‘agnostic’?

Rich text document
OpenDocument format .odt
Word 2007 (.docx)
Word 2003 (.xml)
Word 97 (.doc)

Which will allow me to open on the most different types of devices and operating systems. I imagine it’s one of the first two?

never heard about odt, but the one that can be open on any device is Rich text document, windows notepad, mac textedit or any other version name that might have, open docs linux and android google docs or any program that can open office documents, also google drive and other cloud services have their own file reader integrated with the app, the other one word 2007 because even if you do not have a program installed you can use a cloud storage service and with their own in built tools will allow you to access the file, just remember that the older the format the dificult is for other software to open it, documents from word 97 and 2003, give you some errors with new software versions depending on what is on the word file.