Having two competing OS teams was a bad choice made much earlier by Elop's predecessors, who didn't understand software (the previous Nokia CEO came to that position from the legal department — a terrible mismatch for a company about to be overrun by Apple and Google). Elop was fundamentally right in killing both of Nokia's operating systems. Symbian sales were collapsing in early 2011 because the devices just couldn't respond to user expectations anymore, not because of anything Elop did.
I can see why Elop picked Windows Phone over Android: it truly was a more innovative UI and Microsoft was willing to pay Nokia a billion USD per year for the partnership. Elop's grave mistake was not having a replacement ready to go. The Lumias shipped way too late. Playing "armchair CEO", I have no idea how I would have solved that either.
In any case, Nokia didn't end up too poorly. Microsoft bought the phone division that was bleeding cash, and that money gave Nokia the opportunity to buy back its network division that had been a joint venture between Nokia and Siemens. The outcome was probably better than if Nokia had tried to downscale itself into a commodity Android vendor.