As far as "moneys worth," I would argue iOS. Apple has been pretty faithful to users of older devices when it comes to updates. With Android, your updates experience differs with each device manufacturer. Some are good, some are terrible. LG for example is notoriously bad while Samsung is petty good. A lot of big apps also start their life on iOS and then filter down to Android and Windows Phone. So the experience on the iOS version is often richer and more polished. On the other hand there are also a lot of apps that are free on Android but paid on iOS, so you will have to pay for something on iOS which Android users are getting for free. Angry Birds and Whatsapp are prime examples. Still my vote would go with iOS. Most devs seem to put more effort in their iOS apps.
Google seems to update Android with the high end, latest phones in mind - they don't really consider older hardware that much. They leave it to the manufacturer to somehow make it work on lesser devices. Furthermore, some of Google's latest and greatest features ONLY work on 4.1 Jellybean Phones - which still only make up about 17% of the total Android phones out there according to the stats.
Windows Phone is still a bit behind the big two - and back when they moved from Windows Phone 7 to Windows Phone 8, they screwed over a lot of WP7 buyers because none on those phones were able to upgrade to WP8 even though all those phones were less that 18 months old - it was rather scandalous! At the moment they say WP8 phones WILL be able to upgrade to the later versions, but there are a lot of WP8 devices coming out with only 512mb RAM. Thats quite meager for today's standards, so its another potential screw-over on the horizon. Actually, some Windows Phone 8 apps are already unable to work on such low RAM, so its only the top models that are worth buying with WP8. Pretty lame as a value proposition.