I owned an HTC Windows Phone 8X for a little under a year and a half, and after some careful consideration I decided to switch to an iPhone 5s. First, I have to say how awesome T-Mobile is, and that this switch wouldn't have been possible at this time on any other U.S. carrier. Their lack of plans means I didn't have to wait until I was "upgrade eligible" or anything stupid like that. Since T-Mobile doesn't have plans, they can't do a traditional subsidy either (yay!), so instead they just have straight up financing for phones at 0% APR. All I had to do was pay off my previous phone and finance the new one. I only had to pay $200ish after taxes and fees, which is what it would have cost at the end of a contract on the other carriers, and considerably less than if I had wanted to switch any earlier.
Anyways, enough gushing about T-Mobile :-). So why did I decide to switch? There isn't one big reason, just a bunch of small ones.
When I first bought my phone, Windows Phone 8 was only a week or two old. It was incomplete, but showed a lot of promise. Fast forward to today, and Microsoft just hasn't been iterating and improving Windows Phone 8 fast enough. They seem to be going at the same pace that Google and Apple took with iOS and Android in their early days. That was OK for Apple and Google 5 years ago, because they didn't have any competition, unless you call BlackBerry 6 and Windows Mobile 6 competition.
Microsoft does have competition though, very intense competition in fact. They have to catch up, which means working overtime, and Microsoft just hasn't done that. There are still a lot of missing features that I thought would be here by now but aren't. Windows Phone Blue needs to be release yesterday. It's the same issue with Steam versus EA's Origin service. Steam was a pretty terrible service for several years before it became the powerhouse in gaming that it is today. Origin didn't have the same luxury though. It was released in a state much better than Steam was at first, but it had to compete with Steam, and is now relegated to just being a content delivery mechanism for EA's own games, not a competitor to Steam. Such is the fate, I fear, of Windows Phone.
One of the key missing features for me that led me to switch to iOS is tethering over USB and Bluetooth. WP8 can only tether over Wifi, and tends to be finicky about it at that. Now that I commute to work on BART I rely on tethering every single day, so it is a key feature for me.
There's also the app situation. The situation as it stands now is that the app store is a pretty good size now, and has pretty much everything. What is happening though is that app makers are only putting in a modicum of effort just so that they can get their few WP8 users to stop complaining. There are far too many WP8 apps that are missing key features compared to their iOS and Android brethren to count. I don't know what the answer to this problem is, since most of WP8 success has been in emerging markets that, by definition, aren't big consumers of U.S. centric services.
Another reason I switched actually isn't Microsoft's fault. We have a very Apple-centered household. I'm typing this on a Macbook Pro (on BART, tethered to my new iPhone), we have Mac mini's connected to our TVs, we own an iPad, and Melissa has an iPhone too. Apple products just integrated well together, and my 8X always felt a little left out. If we were a Microsoft household, then the reverse would be true, but unfortunately for WP8 we're not. My 8X was always being left out.
This isn't to say that I'm glad to be rid of my phone. It's the opposite in fact. I loved my phone and WP8. The interface is so good at surfacing important information quickly with it's lock screen and live tiles. I really miss that in iOS. I also really like how the OS presents apps and how you can navigate around apps. App navigation is something of a hybrid between Android and iOS that I think really hits the sweet spot. Their focus on photography with the higher end Lumia lines is also something I really appreciated too, even if I didn't own a Lumia myself.
So I got my new phone with a sense of resignation as much as a sense of joy. The iPhone is definitely the better phone for me, without question. But it's not as much fun. I am going to miss seeing the reaction of people when they ask me "So, do you have an iPhone or an Android device?" (yes I am the kind of person that likes to be different, even though in practice I'm not that different). So farewell Windows Phone 8, I'll miss you, but at the same time it had to happen.