Mace - they're about tied as far as the Force goes, Obi may even be a little better, but you can't deny that Mace is the better dueler. He's more aggressive, younger (which, in some cases, does make a difference), is in better shape, has been fighting alot whereas by ANH Obi is pretty out of shape and hasn;t seen alot of action in a while. A better thread would be TPM Mace vs. ANH Obi-Wan. That one'd be close... not sure who I'd vote for, then.
This fight is very close... on one side you have Obi Wan Kenobi... who has developed more control over the force yet not faced combat in many years... and on the other side you have Mace Windu... great fighter but his control over the force is probably no longer greater than Obi Wan's... this fight to me all depends on whether or not Kenobi's soresu can hold up against the vaapad of Windu. I think that if ANH Kenobi can hold up against Vader... then he should be able to withstand Windu... only just though. This is a very balanced fight.
Just my two cents.
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