Obi Wan would win I think.
Why? Altough Obi Wan sais in Ep. 1 Anakin is stronger in the force he is the superior swordfighter of them both. (Then again, in a one to one battle Darth Maul would beat both of them.)
Sure, Darth Anakin killed Obi One in Ep. 4, but Obi Wan dropped his defences on purpose, leaving him defenceless.