I've settled for iTunes 10.4.1 on all my Macs (5 going back to 2005).
It's the last version that doesn't pester you about not having an internet connection when you start up.
It also allows multiple windows, cover flow, and album art views larger than 600X600.
It's not so good at Apple-Genius-Radio-Cloud-Share-Purchase, or whatever it's called and syncing with iOS 9 point something. Which is why I also keep a copy of iTunes 12.3 around. They share a single prefs file, but I call one iTunes and the other myTunes. you can guess which is which. Only one version can be run at a time, and I have to be careful about holding down the option key to switch libraries when I switch versions, but it mostly works pretty well, both for listening to my library, and for purchasing stuff for and syncing with shiny new devices.