@s15 Well, that's a toughie...!
Both OS have their strengths and weaknesses... So it's hard to declare a clear winner among these two...!
As for which one do I prefer... Well, I personally prefer Android...
It's highly versatile & customizeable platform, looks better than iOS (5.0 Lollipop onward, Kitkat looks rubbish to be honest!), and you don't have to be FILTHY RICH to afford an Android Phone! I love the way you can customize Android with themes, launchers, widgets & stuff... Heck, there's a WP8 Launcher on Play-store that'll transform your Android into a Windows Phone! I mean, I was shocked when I saw this launcher in action!
Unfortunately, it's the least secure platform and quite prone to hacker attacks, viruses and malware... Apps can run in the background and monitor your activity and GPS co-ordinates without you even knowing... Android may have 1 Million + Apps on Play-Store but most are garbage, full of ads, and most unknown apps contain pornographic & adult material... App quality is practically non-existence... If you've used a Blackberry 10, Windows Phone or an iPhone then you'd probably understand what I mean...
On the contrary, iOS is secure, highly optimized and polished... It's a closed sourced OS so no fear of viruses and malware... But it's versatility is not on par with Android... You're stuck with same basic theme, icons and stuff... It's not necessarily a bad thing, but for some it is...
So, long story short; my answer is NEITHER!
WINDOWS PHONE ALL THE WAY!!!
I'm about to update my Lumia 430 with Windows 10 Mobile...! Shall share my experience in my long dead Windows Phone thread shortly!