Windows Phone/10 mobile is the most solid and efficient OS. The only drawback (and it's not even a problem with the OS itself) is the lack of apps when compared to Android.
I use both Nexus 5 and iPhone 6, the only reason why I vote for iOS is because of the garbage dump in android, my observations goes 1 GB ram with iOS equals 2-3GB in android.
Android is the best mobile operating system by a large margin - from apps availability to operating system performance. Not to make mentioned of the huge number of brands associated with it.
The apps count on both platforms is high but Android's Google Play still leads iOS' Apple Apps Store with over 100,000 apps.
I use a Lumia and good old Nokia Asha as secondary phone. I think nothing can beat the battery life of feature phone.
I like Android. It's not complicated and user friendly. You don't need to install a third-party software in your laptop to transfer files. You can easily transfer files via WiFi or bluetooth.
Android is good for me. It is not complicated. There is nothing extra that I can do on ios. Plus android devices are cheaper.
Android ( I am more inclined to android as i am using it from past several years without any hiccups) or iOS as well is equally good as it is constantly growing.
It used to be Symbian on my N8, and now it's WP 8.1 on Lumia 930. Why? Rock steady. Haven't met a single person without issues on Droids.
I still go for Android and as you can see it gained immense popularity because of the wonderful appearance and it is so efficient. No. 2 on my list is iOS which I find very user friendly too.
Android Based OS is getting more popular day by day because of it's exciting features. But when choosing android it is better to choose the previous versions. Latest android OS is Ice Screen (version 4.04) but this OS is still not stable. But version-2 that is OS Jelly Bean is more stable and user friendly.