Ive tried using my Nokia Lumia 1020 aa my main phone, meaning i inserted my active post paid sim card for about a month and i still went back to my iPhone 4s as my phone.
Dont get me wrong. Nokia lumia 1020 is a great phone, BUT i still find my older phone more effective.
1. Lack of quality apps. Actually, popular apps are already available for windows phone. Its just that the windows phone version is vastly inferior to its iOs and android counter part. Example facebook app on wp is slow to update and slow to post. The resolution of the apps dont give justice to lumia 1020's high resolution display.
2. Too big. Lumia 1020's 4.5" screen plus the bezel is too big to comfortably hold and compose messages using a single hand (ive got an average size of hand)
3. Battery life. Im not sure if i got a lemon unit but im only getting around 4-5hts continous heavy usage of phone with 3g/lte on always. Too short!
4. Notification is faster on iphone. I have fb and other app on my lumia 1020. I also have the same apps on iPhone 4s and i noticed that the notifications (specially on messaging/social networking apps) are quicker to appear on lumia 1020.
5. Ease of use. Its just a matter of familiarity on the phone.