Tbh most phones now are generally pretty user friendly. The Pixel I would say from an android perspective is the most user friendly. I find other android phones have too much of a custom skin over and ruin the device.
My nexus has been smooth as hell. Since it's android you will get a bit of freezing now and again but if there gonna be any device that runs smooth, it'll be the Pixel.
As the famous Apple slogan went "there's an app for that" but if it's a Word document then Google Docs does open .docs files but you can get Microsoft Office on the Play Store so could easily continue what ever file you are using.
Screen to Screen transfers? I'm not sure what you mean sorry?
Google Play Music is the default music player and on the Nexus it's fine, kind of like Spotify with the option to listen to your own music as well, as well as uploading it to free up space. The 6P has stereo speakers so anything sounds good on that. The Pixel I can't actually say as I've never heard it but from what I've read, it's a downgrade from this phone but that's only the speakers on the phone. If you are after a phone with top of the line audio through headphones then I'm sure Sony and LG use better DAC for that. I think android plays FLAC files natively as well so if that's your thing you're good on that. If you're on about using equalisers, there's plenty of options and most alternative music players in the app store have their own built in one. If you're willing to root then you can go one further and get very, very equalisers that make your phone sound amazing but that involves some technical knowledge.