I don't want to compare speed, user-friendliness and similar things the internet is full of.
I'll compare something that's personally quite important to me: battery life.
My HP has a standard 55Wh battery and an extended 92Wh one. Both have been in use for a few years, so their capacity is long past what it used to be. When both were new I could work without a problem for 15 hours. In Ubuntu, working on battery for 7+ hours is no problem. My system isn't optimised and I haven't looked into what services are running. With Windows I'm happy to get 5 hours... I've disabled unnecessary services; what doesn't need to run, doesn't.
I can't understand what makes Windows lag so markedly — the difference isn't just a feeling, it's noticeable. On top of that, Windows apparently can't understand that I have two batteries. This leads to a situation where even though the first battery still has enough capacity to run the system, I get a critical battery warning...