getattr() versus __dict__ lookup, which is faster?

I can dynamically look up object attribute values using object.__dict__[some_key] or getattr(object, some_key). Which is faster or better, and why?

>>> class SomeObject:
...     pass
... 
>>> so = SomeObject()
>>> so.name = 'an_object'
>>> getattr(so,'name')
'an_object'
>>> so.__dict__['name']
'an_object'