Since getting used to using modern IE 11, I've been spending most of my time on the SP3 in modern. The only time I switch to the desktop is when I'm managing files (I just can't get used to the modern file manager), using Office 2013 (which is actually seldom on the SP3), or when I simply have to use Chrome for some reason (e.g., sending pages to my Kindle).
I use the desktop about 50% of the time on my desktop machine (no pun intended), because of video editing, much higher Office use, and Quicken. Even there, though, I use a fair number of modern apps, including modern IE. Once I got used to using modern apps, I just liked their functionality more than I expected, and so if there's a modern version, I tend to use it.
Windows 8.1 has really gotten a bad rap IMO. It's much better than it's given credit for.