All I've ever used is the 1/2 inch one (and as far as I can recall all my rulers are 1/2 inch extra on one side). Can't say I've ever seen a 1/4 inch on both sides ones.
I like the 1/2 inch on them and can't imagine using one that has 1/4 inch on both sides honestly. But I do think it is whatever you are used to using and/or comfortable with.
Thanks for the heads up to watch how rulers are marked if you are buying a new one!