Both operating systems support multi threading, You are probably thinking about multitasking, which is also supported by both operating systems at the moment. The fact is, both operating systems are very similar nowadays, what you really have to compare is the ecosystem. iOS still has a better ecosystem with more high quality apps. Android has caught up in quantity, but not so much in terms of quality, yet. But that's not a feature of an operating system, just market forces and economics at play.
Personally, I gave Android a try yet again this summer by switching to a Moto X Dev edition. One key feature for me is the ability to highlight text on the screen and have the phone read it to me. After many hours of trying to set this up with the use of some 3rd party programs, I gave up. It worked, but not reliably, and only by using the clipboard, which wasn't a good solution for me. That's really something that should be a 1st party feature, like it is in iOS. Other than that, the OS is solid. I ended up switching back to iOS in the end. For me Android is still much to ugly, but that a personal preference. To each his own.
You should give both operating systems a try, before making up your mind. It sounds like you haven't. Also, don't forget that there is Windows Phone 8 and Sailfish OS, both of which, though very small in terms of ecosystem size, are very interesting and innovative operating system, especially when you compare them to the stale looks of iOS and Android. But that's only if you are actually interested in learning about Mobile OS design, as apposed to just starting yet another fanboy screaming match.