I've used Android (Nexus line up until 5), and Windows Phone (up until Lumia 1020) fairly extensively. I'm currently using a S6 Edge. I use iOS for work, as that's what they issue (ipads and iphones).
Here's my take:
Windows Phone, in a vacuum, is generally a more user-friendly OS. Android is the least out of iOS and WP. But, the app gap is a very real issue, and the single largest reason why I could never get comfortable with using a WP device as a daily driver. If it had near-equal footing with Android and iOS on the app front, I probably wouldn't ever even give Android a second glance. Obviously, the app gap...gap is going to differ from user to user, but for myself, virtually non of the conveniences of mobile computing were available on my WP (online banking, credit cards, virtually anything google related, various smart home products, etc). I really don't give a hoot about mobile gaming, so that side of the app gap never bothered me.
There are certainly things I miss about WP now that I'm back on Android. First is the simple integration of Cortana for developers who took advantage of it. Google Now is more useful as a stand-alone, but pretty much utter poop when it comes to integration with third party apps (outside of some very specific ones). Doing something as "simple" as voice control of my Hue lights is a huge ordeal on Android, requiring multiple programs and profiles and code. And, while I like the spirit behind being able to "hack" together solutions, I just think back to how a developer was able to just make it work with Cortana, without any work on the user's part on my WP. This is just one of many examples.
I don't see that app gap closing any time soon. Microsoft clearly doesn't consider WP a priority, and is far more focused on being the software company they actually are and pushing their services to be as platform agnostic as possible (which makes sense).
Android's update philosophy is complete bonkers, and was the main reason I'd stuck with the Nexus line in the past. The sexiness of the S6 Edge won me over to the dark side, however, but who knows if it'll ever see Marshmellow or anything beyond.
For non-gearheads, I generally just tell them to get an iphone. Android just isn't quite user-friendly enough imo for the completely tech-illiterate, and even with all of Android's market share, iOS is still the platform of choice for the majority of social types, and still mostly the first (and sometimes only) destination for most "new" apps and ideas.