Crestor is a statin (rosuvastatin calcium) only,
Vytorin is a statin (Simvastatin)
with Zetia (ezetimibe). Statins work by controlling the production of cholesterol in your liver while Zetia works by preventing cholesterol to be absorbed in your digestive system.
Of the two, Crestor is the stronger of the two. In addition, recent trials have shown that adding Zetia does not improve the performance of Vytorin over Simvastatin alone.