I was just reading a forbes article on this. Absolut Vodka used to be the trendy drink and now it's being challenged by Grey Goose and Belvedere for market share. The article also says how most people can't really tell the difference.
They brought in an expert taster and he ranked them as follows
1. Absolut - Rich texture, smooth
2. Level (by Absoult) - Vivacious and syrupy in texture
3. Grey Goose - Neutral in smell and flavor, short, silky
4. Smirnoff - Fairly smooth, a little bite, peppery
5. Jean Marc XO - tastes like pine sol