Amps schmamps I say.  A vacuum that causes all the lights in the neighborhood to dim when you turn it on is no guarantee that it will remove all the embedded dirt from you carpet.  Amps, horsepower, sealed suction, airflow, nozzle shape or anything else by itself is not an accurate measure of effectiveness.  There are lots of variables involved in how well a vacuum does it's job but that's way too complicated for the average consumer who just wants a quick answer.