Tough question. I have been using smartphones ever since they came on the market, hence way before the iPhone was launched. I started with Windows Mobile devices, but when Microsoft stopped development after WM6.5, I switched to Android and used it for five years straight until last year. Last year, I purchased the Lumia 830 directly when it was launched.
My main reasons for switching to Windows Phone (WP) were:
1) I always found Android a bit messy, i.e. no consistent feel/experience thorughout the interface. This is probably the result of Google not applying very strict rules on apps & widgets. In contrast, iOS and WP are very consistent, which I personally like a lot.
2) The main reason however is that WP ties in much better with my professional workspace as everything is Microsoft at work. Since I work at a large company with very strict IT-security, it was always a struggle with Android. All kinds of work-arounds had to be developped since the native support is not that great on an Android device. iOS and WP on the other hand integrate perfectly with full native support.
3) I always liked the interface of WP with the active tiles.
4) I always liked the Nokia Lumia designs.
So, I have been using the Lumia 830 now for almost a year and I am still impressed by it. The OS is extremely stable, and everything simply works. I never have battery drain issues (Android.....) and I absolutely love the fluid integration with my professional workspace. In addition the camera on the Lumia 830 is very good, really nice pictures also when the light is not optimal.
But, there are things that bother me and actually I notice myself getting more and more annoyed over time. In all honesty, these have nothing to do with the Lumia 830 itself, but more with Microsoft and the way they manage the whole WP-program. For example, I live in Belgium, and still have no Cortana. I know I can get it by changing regional settings, but apart from messing up my acces to the local WP-store, it is ridiculous that one year after launch nothing has changed. Microsoft seems to completely ignore the non-US markets even though it is exactly in these markets that WP is getting some traction and market penetration.
The other thing annoying me is the much discussed and debated "app gap". I know, it is all relative, and some people are more impacted than others, but to me local apps are important and its is exactly there that the app gap becomes most noticeable. I mean, have you ever seen an add for an application from a company, a school, a local retailer, you name it, where anything other than the Apple App-store or Google Play were advertised???
Third thing is accessories. It is very tough finding cool accessories for any other smartphone than the iPhone or Samsung Galaxy S-models. And I am not talking about cases, but things like smartwatches and fitness-bands, or other cool bluetooth enabled devices that can actually connect and share full functionality. It just does not exist for WP, the only exception being the Microsoft Band, which again is extremely difficult to get if you do not live in the US (rest of the world is again seemingly irrelevant to Microsoft).
Apart from the Lumia 830, I also use the iPad mini 2, which is also fully connected to my work-environment. So, I do have plenty of experience with iOS to know that it is just as stable as WP and very well executed, I mean, it is one consistent experience troughout the device. It think it is actually very ironic that Android has the largest market share of all three OS's, while being (in my humble opinion) inferior to both iOS and WP, purely looking at the OS itself. But history repeats itself, in the old days VHS was also the inferior system for videorecording compared to Betamax and Video 2000 but yet the most used standard.
So that brings me to the basic question: should I buy another WP or not? To be very honest, I am very inclined to switch to the iPhone for the very reasons listed above. In my heart however, I would hate to do that as I believe WP is a superb OS and in fact closest to my likings. Microsoft however, is making it very hard to love them.
So most likely, I will wait until the official WP10 upgrade comes to my Lumia 830 and wait a bit to see how I like it, but most importantly, if WP10 really brings changes on the "app gap" front or not. If not, then I will make the move to iPhone where at least I know that full support exists from softwaremakers, and accessory makers.
Just my two cents.