MS Office has clearly had more thought put into the UI. I often find with Libre (I haven't used OO in a couple of versions so it may have improved). LibreOffice Writer always feels a little clunky, it's like older versions of MS Word that made certain things difficult to work with. An example I hit the other day... at the top of a new document, insert a table... now try to delete the table... after several minutes trying I had to create a new document and paste back everything apart from the table. This is just one thing that I remember from recently, working with complex layouts and floating boxes can sometimes be a bit of a pain, although mostly I've only done that with documents that were created in Word so wouldn't expect them to work 100%.
Having used both MS Office and LibreOffice extensively, I just find fewer situations where the application is getting in the way of what I'm trying to achieve.
LibreOffice Present also has some rather odd quirks if you're working with ppt/pptx files. On several occasions I've saved a .pptx file, opened it back up and all the font sizes are different and every line has a bullet point in front of it, it's just little things like this which make MS Office a little better.