M, RS, V, F, AMG. The alpha alphabet represents five manufacturers' best efforts to create something unique, exciting and memorable from their more prosaic mainstream motors. The resulting "performance tuned" sports sedans are so powerful, so capable, so versatile, that they're the ground based equivalent of the all-weather fighter jets that battle for control of the skies. While the shibboleth "there's no such thing as a bad car" applies here, there are always going to be winners and losers. And it's our job to sort the wheat from the chaff.