To the OP:
I'm a big MS guy...and even enjoyed the Windows Mobile days. During the WP7 days, I was on BB and IPhone. I switched to WP8 two years ago. First with the 920 and then the 1520. I travel a lot for business and use MS Exchange, so WP8 was great for me. Recently, I asked myself the same question you are asking yourself. Do I stick with WP or wait for it to mature and go with the IPhone (which my wife has). I also have 2 kids (ages 1 and 2.5), and although the 1520 Lumia camera is better than the IPhone, it still takes 3-4 seconds to take a picture. This was very difficult for me since both kids do not stand still to pose for more than a second. Outside of the App gap and any other downsides of WP, the long camera delay on my 1520 was causing me to miss moments in my kids lives while my wife would snap 10 pics (great quality) in seconds using her iPhone 6. So I compromised and kept my 1520 has a secondary and got the IPhone 6 Plus as my primary.
Having used the IPhone 6 Plus for the past 5 days, I have to say I'm impressed. Today, the IPhone has almost all MS ecosystem apps on IOS. OneDrive auto backup works great. Office (Word, Excel, PPT) are on IOS. MSN News, Sports, Travel, etc. work great, if not better on the IPhone. The Xbox One App is works just as well as the WP8.1 app. I prefer to play with W10 on my 1520 and hope that developers support WP in the coming years.
Finally, I will end with this: Yes, we all know there is an app gap, and quite honestly, that is another reason I made the switch to IOS. When banks are pulling apps from WP, it becomes frustrating for the user (and I do no think going through the hassle of switching banks is the correct solution). We have seen many official apps arrive to WP (which is great), however I noticed something interesting while using the IPhone for the past few days. The level of how much apps are updated and maintained on the iPhone is amazing. For example, FB or the ESPN app could have been updated two days ago, and then again yesterday and then once more today. The level of attention given to the apps and the user experience in the iPhone is not seen on WP. WP's apps are updated sparingly and sometimes months go by before we see one.
The choice is yours and what makes you happy. As one commenter stated on this thread, choose the device that has everything you need today and not what will come later. I do miss the live tiles, but the widgets on the today section on IOS (including the notifications) come close. And the Lock Screen notifications (including the ability to reply to an SMS from the lock screen) on IOS is awesome. IOS is poor on contact integration, especially FB. I miss the social contacts integration from WP the most. Anyway, I will continue supporting WP with my 1520, but no one ever said that you cannot taste other flavors.
Good luck on your decision and I hope this helps.