The difference is that:
the variable names with _ are instance variables.
self.variable is calling a getter method on your object.
In your example, the instance variables are automatically generated and you don't need to synthesize your properties either.
The real important difference in your example comes into play if you are not using ARC-
self.variable will retain an object for you if you mark the property with retain or strong
_variable does not address memory management at all
