I've got a S7 Edge and if there were a model of Windows Phone with current hardware, I'd dump the S7 Edge and get one without bothering to think twice. Android's UI is miles behind Windows Phone, particularly the live tiles and the mail UI.
Android slows because of ton of crap that can be installed. WinUP is clean as no one makes crap.
I have a nexus 4 with no play store. Juat installed whatsapp apk directly fron whatsapp.com. at least 3 day battery time.
The Windows/Tile UI is very polarizing and one of the major reasons for the failure of Windows 8. I personally dislike it.