I've jumped around for four years between BB, iPhone, WP7, Android, WP8, and now back to iPhone, having ordered the 5C.
I originally bought an iPhone 3G in 2009. I liked it, but after several months I downloaded the new iOS version (I forget which one it was). Apple said that it would run on the 3G, but it made the phone slow and laggy. I was so annoyed that I swore "never again" for Apple. (Now that I'm slightly more savvy than I was about smartphones, I realize that it's probably not the best idea to download a new OS onto a two-year-old device.)
Having tried WP and Android, I'm now excited to be returning to Apple. I liked WP, and found the graphics and style strongly appealing. My problem was the apps. I never used a ton of apps, so although I knew going in that there wouldn't be the same app availability as Apple's or Android's, I didn't think I'd have a problem. What I didn't realize was that you don't have to be a heavy app user in order to have an app problem on WP. If one new service/app comes out that you really want to use, and you can't because your smartphone platform doesn't have that app, then your experience of the phone is significantly impacted, and now you have an app problem.
In my case, the last straw was Uber. I grew up in NYC and never learned to drive, and my current job involves going to different locations in my metropolitan area every day, so I rely a lot on public transportation. Uber would be very useful for me, since sometimes I need to get to locations that aren't served by public transit. But Uber only has an Apple and an Android app. They did have a WP app for a short while, but it was only a web wrapper and received such wretched reviews on the Microsoft app store that Uber pulled it. I realize I could use the Uber's mobile site, but it surely wouldn't be as easy and pleasant to use as an actual app.
Now that I'm waiting for my iPhone to arrive on Friday, I've been researching what apps I'll want. I knew Apple's selection would be better than Microsoft's, but I'm shocked by the vastly greater quality and quantity of apps. It seems like developers are simply not going to devote the same resources to developing for WP as they do for Apple and Android, if they even bother developing for it at all.
I also grew frustrated with Microsoft's seemingly glacial pace in terms of updating their phone OS. It seemed like they were only ever going to allot a certain amount of resources to WP, and no more, and all of those resources were spent in improving the software to handle new hardware, with very little being spent on actually improving the user experience. It's nice that Microsoft just invested $7 billion in mobile hardware, but it would have been nicer if they would have spent even a fraction of that over the past two years on improving the OS in ways that users would notice. WP8.1 will be out next year, so there will be some improvements there, but Microsoft has a lot of catching up to do and they don't seem in very much of a hurry.
I'm still enamored of the WP interface, though, and I do think a Windows Phone would work well for a lot of people who really don't need to use apps at all, just the main smartphone functions. I wish Microsoft well, and I hope those users who are patient and loyal enough to stick with it get some good improvements and app progress, which they certainly deserve. I'm very much looking forward to using iOS 7 for many of the same reasons that I like WP -- I love the whole flat-bright-color thing, and the thin, sans-serif typography.