Should i get Otterbox Defender or Commuter?

I'm getting an iPhone 4S tomorrow. I'm not a very clumsy person but i do drop my iPod touch occasionally. I want a case that allows my phone to still fit in my pants pocket. It needs to be a sturdy phone and i will put my phone in my backpack for school. Thanks!

Added (1). Needs to be a sturdy CASE not phone

The defender is more sturdy but it's really bulky and ugly. Might not be able to fit it in your pocket. I find that the commuter works pretty well and is far less bulky/ugly