I came from an HTC 8X running Windows Phone, which was my first smartphone. I really like the WinPhone OS. The 8X has a very clean, sleek design.
However that design us flawed. touch screen is very exposed; I'm glad I had the protection plan because the glass cracked about 4 times in 2 years, and only one was an honest-to-goodness drop. They others.... it just cracked for no apparent reason. Also, the volume and camera buttons are flush on the edge of the phone. After two years I still couldn't push those buttons by feel, I had to look.
Like I said, I liked the OS, but the lack of apps was a deal-breaker. Everywhere I saw a sign that said "download our app!" it never included WinPhone. I managed to find apps to do whatever I wanted, but sometimes had to settle for second-best - no Strava to record bicycle rides; had to settle for endomondo, which was okay, but everyone else is on Strava. American Airlines had a sweet app that let me easily get boarding passes, but then they discontinued it. I got a Fiat and they have an app, but not for Windows. You get the idea.
I decided that when I got a new phone I'd try Android. If I don't miss WinPhone, I'll probably stay with Android; otherwise I may go back to WinPhone next time around. Supposedly when WinPhone 10 comes out it will be able to use Android apps. But until then, apps are still the deal breaker.
This week I missed some texts from my wife because the MMS got messed up on the 8X and it was time for something new. I chose an LG G3 and it arrived today, but after reading about the G4 here I decided to take it back and go with the G4.