I haven't found a huge difference between them.
Tuthill claims that their Competitor series blowers have more airflow than the ones they were designed to compete against... and I verified that when I built a SplitSteam with a Tuthill and a Roots facing each other and turning at the same exact speed, through mirror- image plumbing back in 2000. The Tuthill did have 30 CFM more, which, for a 33 / 3003 / 3M, means that it was about 15% more airflow than the Roots.
Roots does have "DSL", by the way, Greenie... "Dual Splash Lubrication"...