Wow lots of replies.
I've been using my iPhone 6 for a while now after a brief stint with the S6 Edge. I've had my fair share of Android phones and iPhones. Never got to actually use a Windows Phone.
LOVED my old Blackberry Curve + Bold and still want one (might pick up a Passport Silver Edition if I can find one for 300 or less)
My launch day M7 was glorious. It was new. It was fresh. It had awesome speakers. Unibody metal design. I really thought HTC was going to take Android places. I still have the phone and would use it if it wasn't a slow POS now and battery/camera didn't suck.
I don't really take sides of one or the other. Just use whatever I like most at the time.
My personal pros for each OS/Manufacturer
Android
Back Button - SO GOOD
Variety - It's great having so many different phones I can try but a lot of them are budget crap and/or just really doesn't excel in areas I want. But variety is always a plus.
Removable Battery - I think this is such a great feature on Android. Especially with the planned obsolescence on devices these days. Much better feature than stupid things like slow removable storage.
File System - Another great feature I can't live without which is why I can't ever drop jailbreak from my iPhone.
Direct downloads from browser - Same as above.
Customization - Skins are atrocious but being able to use launchers/rooting/tweaking easily more than makes up for it.
iOS
iMessage - Simply the best messaging app out there. Best UI. Lightning quick. Elegance and feature packed in one package. Nothing even comes close (trust me, I've used nearly every messaging app out there). FB Messenger is pretty good but I don't use FB anymore.
Ecosystem - The apps are second to none. A lot of apps run and look better on iOS. This is not a bash on Android but more at the devs. They also got a lot of the niche apps down which I can't find on Android.
General polish - This is something I can't stress enough. A majority of their built in apps look and work great. Things as simple as the dialer, calendar, keyboard, calculator, weather, camera, notes, stocks, music, podcasts, etc etc, all work amazing. I don't need to go on the App/Play Store and find a better version of a simple thing that should just work out of the box. Why do I have to deal with setting up something stupid like visual voicemail? Simple, functional and a good UX is all I need in my basic apps. I'm guaranteed a great camera, screen and battery. Something I can't say about Android.
3rd party support - Just because the iPhone is so popular, it gets immense support from 3rd parties. Can't say the same if I bought something like the Nexus 6P. I feel like I bought a Nintendo console when I buy an Android device unless its something popular like the Galaxy. It was a struggle finding nice accessories for my old HTC One, Nexus 5, etc, aside from cheapo cases on Amazon.
Blackberry
No frills. Great email and messaging apps (albeit the og king of messaging; BBM is no longer relevant). Legendary keyboard. That colorized LED notification light. A lot more tolerable now with support for most Android apps.
I honestly think Android just needs more premium handsets like the S7 Edge with slightly more polish and they could really do some damage. Wishful thinking though.