Maybe it's just the crotchety old man part of my personality but I don't like anything after Office 2003. The ribbon interface is a deal breaker for me.
Office 97 is the last version I ever bought or used. I used it for a decade, or so, to open those few files that didn't work quite right in OpenOffice (or AbiWord or KWord or whatever other program I was using back then on Linux). I'm glad I haven't had to open MS Office in about a decade. These days, I keep LibreOffice installed, but use it maybe a couple of times a year; Google Docs does everything I need.