When you consider apps, android is the best choice. You can get number of applications for android that too for free. For some pro apps we need to pay some money to download but that's OK. When it comes to security, Windows has strong hold compared to Android. But you can still safeguard your android device by using any good antivirus applications..
If you take into account the ease of use of the operating system, then windows phone has a more straightforward menu, but the android is more common and support for Google Play. There are already more that like it.