While I've never tried it with
sake, I've experienced that the
rice vinegar method tastes a lot better if add one tablespoon of
sugar and one teaspoon of
salt (per tablespoon of vinegar) to the solution. Let it boil up briefly and cool down, then mix it in with the rice.
As magenta so lovingly pointed out, the above can also be used as a recipe for Mirin if the Rice Vinegar is replaced with Sake.