I've never used a Blackberry, so have no standard of comparison, but would like to make a few comments regarding some of the things in this thread.
First is the rivalry between owners of WP and Blackberry, which covers neither community in any glory. If Blackberry does end up a 'dead platform', it won't make me happy. Quite the contrary, I'd like to see Windows Phone, Blackberry and a resurgent Apple take the battle to the Googlemonster. When I opted for Windows Phone, it was for positive reasons and experience has proven that that decision was the right one for me. I'm convinced WP is the best OS overall and best suited to the needs of the average user.
I am one of the people who would like to see a notification centre in WP, but it is not the deal killer some would have you believe. This is because the start screen in WP is the notification centre. Once past the lock screen, you are presented with tiles which give you information without having to open an app and developers have been very successful in using this capability to provide a fluid and refreshing UI. My one gripe is that if you miss a notification when its posted on the lock screen, there's no way to find out what it was.
I have yet to find a single convincing reason why full multi-tasking is useful on a phone. On a computer, you could use multi-tasking to check your email while Excel is crunching numbers or even watch a movie while generating a Mandelbrot scan, but where is the mobile equivalent? Windows phone does do somethings like play music or download files in the background, but I've yet to see a user task that works that way. As far as I can see, Microsoft were right in limiting the ability to multi-task - every task running uses battery and processor resources.
On a related note, the ability to close apps is redundant in Windows Phone, because when not on screen they don't use resources. The system is designed so that you don't have to manage apps, so when you've finished with an app you just hit the Windows key and move on. If you want to go back to an app, then hold the Back key and swipe to the app you want - the system will then carry on from where you left it. If the system needs more resources, it closes the least used app by itself. I do wonder if that is why I've never suffered the 'other storage' bug, because I use the device the way it was intended.
The app question is an odd one for me because I can't understand why Blackberry would taint perhaps the most secure platform of all by enabling it to run malware. By enabling the side-loading of Android apps, Blackberry have opened a can of worms. One of the reasons I denounce Android is that it is a completely open ecosystem, meaning that there is no protection for users - especially non-technical ones - from hackers. What's worse is that whatever virus protection runs under Android does so without any special privileges, which is about as useful as a chocolate teapot. Why Blackberry went down this route I'll never know. I am truly mystified. Also, I have never felt the app store to be restrictive.
The ugliest word in this thread is bias. If I had Microsoft shares or were payed for every device I sell, then it would be right to say I was biased, but since I see no pecuniary advantage from your purchase I repudiate the charge. Partisan yes, biased no. This is a Windows Phone forum.
So here are my reasons you should choose the Nokia:
i. The camera is radically better than that offered on any other mobile phone with the exception of the Lumia 1020..
ii. The Here mapping services are superb. A friend of mine used his new Lumia 920 instead of his Tomtom and is now selling the Tomtom because he thinks the navigation service is better on the Nokia.
iii. Web services. As well as Xbox and 7Gb of free cloud storage, important information like contacts and calendar are synchronised automatically and available on your Windows 8 PC or tablet. Using Outlook.com, you can set up multiple calendars, including customizable recurring appointments and have it all synchronised on your phone. All colour-coded, of course.
iv. I've used Windows Phone devices for over two years now and they have all proved exemplary. Reliable, gimmick-free and easy to use.
v. Like iOS, Windows Phone is a walled garden. Every app in the Windows Phone store has to pass stringent standards and is vetted by Microsoft. This means you don't need technical knowledge to safely use Windows Phone.
vi. Windows Phone has a bright future. While many detractors have fixated on the 3%(now 3.9%) market share, they do not appreciate that WP is an integral part of a coherent plan - called the 3 screen strategy - Microsoft has for the future. While many companies are innovating, only MS plans to integrate Windows devices into a seamless whole which will enable many new possibilities. Buying that Nokia will put you on the crest of a wave of innovation which is nothing short of exciting.
This is all of course, opinion. Whatever you do choose, I hope it serves you well because I do know what it's like living with a device you hate for two years.
Good luck.