This one really is a good question but the answer is Both. Since the answer depends on whom you ask.
Android os which can be customized a lot and we can update the firmware as per our wish Since its completely open source you will get more updates/apps/games than other mobile os. you will have plenty of options to chose from(in free/ paid apps). Note :: Apps are created in common for all Android smart phones so some might not work in our phone due to hardware limitations, screen size etc.
Windows os is highly standard and a decent usage you wont be given more privilege to customize it. They have some periodic updates and free apps (not as much as Android ). you cant update the firmware.
For a decent smart phone usage windows is a optimum match and Android smart phone along with ultimate access to customize it