Grey Vetiver is the better frag.
Guelain Vetiver is the more classic with a sharper citrus and toned down tobacco vibe in the background.
Also look out for Guerlain Vetiver Extreme. I just got it, and to my surprise it's quite good.......
These 3 vetivers along with Vetiver Extraordinaire from Malle, L'Occitane Vetyver and Encre Noir from Lalique are my personal favorites.
I still need to sniff out Givenchy Vetyver though - head it should be quite awesome too.
If you want a really different vetiver frag, I can highly recomend this one, which smells of incense, fruit and vetiver - a quite masterfully made fragrance IMHO, and I just bought in on sale at the L'Artisan online shop for only £35 for 100 ml
L'Artisan Coeur de Vetiver Sacre - a quite unique scent.