Okay, so I have been a really heavy iPhone user for the past 4 years, had an iPhone3G, then iPhone4. Jailbreaking them, and doing all kinda stuff to the system was a must to me. But then, around 7-8 months ago, I got tired from all that. I set the phone the way I wanted and that was it. However, around that time, my wife broke her old Nokia 6700,and I have decided to buy her a Lumia710. She is so in love with that phone (it is pink, or to be correct magenta), and I have fallen in love with the OS. So smooth, so stunningly fast.
Now I always hated Android for its stuttering, and hiccups, and it ain't a choice for me. Then I started severely thinking about a Lumia920. And, I sold my iPhone, and got myself a Lumia920.
Okay, to me there are some pros and cons in using this phone or the iPhone, so let me try to be objective, and to summarize this:
Both phones r have excellent finish, and that premium feel in ur hand, maybe slightly the scale moved toward iPhone. On the other hand, the screen is clearly better on the Lumia.
Now the main difference is the OS. iOS is jailbreakable (up to 6.1.2 for now), and that means more customisation. I love the Live Tiles and Live Apps on Lumia, and that static screen on iPhone looks so outdated, BUT on the other hand, iPhone has something we Lumia users can just dream of 4 now - SOUNDS: yes u can have custom sounds for messages (even for different senders), and u can have custom vibration patterns, yes u can make that every app that sends a push notification has it own sound... For me that was trully a feature from the future, my phone was beeping all the time (yeah, I get a lot of different notifications), but thanks to differents sounds I knew when it was urgent to look at my phone.
Now we come to the last part - Apps: the AppStore on Apple has around 750k Apps, and the WP Market has around 140k, 5.5x less

There r good apps on the Market, but there r some excellent apps on AppStore. Personally I miss several of them - Teamviewer, Campbell's Operative Orthopeadics and Clinical ORthopaedic Examination.
And now, the icing on the cake, the reason which I left iOS for WP - Social network Integration - absolutely superb on WP. Other OS can just dream of this. For the first time, everything here on my phone, without dedicated apps that do crappy job, everything is smooth, and just like I wanted it to be. The people Hub is an amazing thing 4 me, it is beautifully updating and notifying me of everything I need to know, and all that with just a glance of my eye on the stunning screen. No need to open an app for that. Apps of this kind for me are a thing of past!
So the conclusion: which device I would recomend? Depending on the needs - if u want apps - and I mean tons of them, go for the iPhone. If u want a beatifull OS, still a bit poor in apps, but with all the basics implemented into the OS itself, look no further WP8 is just for u, and ofcourse - Lumia920 as the flagship device is a logical solution.