>>over this side of the pond if I had to pick the most popular it would be Android by a mile

And in the Android camp, Samsung's share exceeds Apple + WP together.

If you look at how big vendors handle cross-platform including very large companies that made their fortunes via the web, they write bespoke apps for Apple and Android. If you really want cross-platform then that's the precedent- unless some other vendor incentivizes you to use their hardware and systems in defiance of the market. When you consider that just one Android device vendor (Samsung) dwarfs all the non-Android players put together, rationally you want to target Android followed by Apple if the goal for users to BYOD. If it's a tablet app or employees are to be provided with devices- then again, unless another vendor provides financial inducements to use their systems, Android is the way to go. In which case Xamarin may be a solution for a problem you do not have...