Smart phone opportunities

Question

Of the two smartphone operating systems, Windows Mobile and Android, for which is there more opportunity? I like the idea of Windows Mobile since I already know the OS and the language and such. I also like the use of Linux as Android. I am not sure which one has more opportunity.
 
The main thing that makes this relevant is that my phone is ready for an upgrade. I am not sure whether to get a Windows Mobile phone or an Android phone or a less expensive phone. A smartphone would be a reasonable choice if I were to develop for it's operating system but otherwise I prefer to use a netbook or something such as that instead of a smartphone.
 
A related question is if there is limited opportunity in the sense that if I develop a successful application, isn't it likely that someone else will do the same?