If Windows Phone has anything going for it, it's stellar speed and stability. My Lumia 930 and my wife's Lumia 830 are rock solid and fast - always. If the majority of your time is spent on the basics -- phone, text, email, web, facebook, netflix, games etc - it's the best platform out there.
That said, the OP's question of "Fully Featured" and "Just Works" are pretty tough to reconcile. Most iPhones I have used or see are less stable than the Lumias -- but they can do more, through their app catalog and integration across Apple's vertical ecosystem. [Insert favorite Android model here] is going to be more capable than anything else out there, but it's been a long time since I've seen an Android distribution that didn't lose control of background tasks and require a fair amount of overhead to keep the thing functional. Windows Phones are definitely more stable and consistent over time, but they don't today have the long tail of apps that Android has or the guarantee that everyone is going to support them that Apple has.