In reply to Alan_2468:
depends what your using it for, mentally viualise how would be the easiest way for you to ascend a rope (presuming thats what you want it for) remember you need it so you can sit in your harness or able to transfer the weight on to the other leg so you can move it up.
but in essence no it doesn't matter, they both do the same thing just one is more ergonomically suited for one hand than the other.
Long words
hope this helps