I've been using a Windows phone for the past 2 1/2 years for 3 reasons:
1) I don't like Apple. I despise using any product that forces you to make chooses simply because you're locked into it. It's been a good business model for Apple, but I like to choose what I think will work best for me, not have Apple decide. Mostly, I dislike the attitude of many Apple users. There's a certain "I'm better than you" air they give off because they think using Apple products makes them superior. They would never even consider any other product, regardless of how much better it might be, simply because there is no Apple logo on it.
2) I don't care for Google. I have a problem with any company that doesn't give me the choice as to what happens to my data. Most people carry on blissfully day to day not realizing that Google monetizes their data. Sure, Google has lots of free products that are mostly well thought out and work as expected. But nothing is free. Every product Google gives away is designed to track you and your data in some way for the purpose of advertising. Remember, Google is a business, not a charity.
3) Lastly, I like Windows Phone. It's fresh and different. There are a number of things it does that its competitors aren't doing, as well as things others are doing that it can't. But overall it's a solid operating system. And I like Microsoft. I like the idea that they allow me to give them access to as much or as little information as I choose. And I believe this is not the same Microsoft many of us grew up with. This is the new, more humble, let's-listen-to the-customer Microsoft. Are there some apps missing? That's been well documented. But I've never felt my life was destroyed because I don't have a Snapchat app. In fact, because of their CEO's attitude towards Windows Phone I'll never use Snapchat. At the same time, I have more quality apps on my phone than I have time to use them. Many of the great apps I have go unused. 90% of what I do on my phone is text, email, browse the internet, check the weather and stock market (just as stormy as the weather lately--thank you Greece), take pictures, and make calls. Windows Phone does these things very well.
So why do I think you should choose Windows Phone? It's about not getting locked into Apple's closed ecosystem or getting raped by Google. And it's also about enjoying a fresh, clean OS from a company that wants to be known for keeping your data private. That's a win-win for me.