Since you're on Win7, I'd say stick with Office 2010. Those two would have been developed around the same time, which helps with stability between OS and apps.

I've used Office 365 since it launched, here for what it's worth are notes I made re the main Office changes over the years:

- What Office 2013 has v 2010
- More sharing plus device and cloud integration.
- Improved interface.
- Some touchscreen functionality.
- Collapsible ribbon.
- Customizing ribbon easier, relatively simple now.
- Word - PDF editing.
- Word - better DTP features.

- What Office 2016 has v 2013


- Nothing major, nice changes. Built from the ground-up with mobile and cloud users in mind, good for teams.
- Core products get a "Tell me" function which is useful.
- Excel got rid of the dumb all caps ribbon text.
- Improved colors in interface.