rylla wrote: Marseilles"Ancien Tarot de Marseille" ("ancient Tarot of Marseille") - grimaud version.
This one and RW (US Games) are probably the most know and sold (I've read that 400 000 copies of Grimaud's Ancient Tarot Of Marseille were sold each year not so long ago).
With their different editions they probably fill the five first positions in the topmost sold (and used) Tarots.
Don't forget the Swiss 1JJ though, as a variation on the Marseilles. Many people started with that one because of its ubiquity here in North America. I think it's still the most frequent offering on the U.S. ebay by far (though some sellers insist on listing it as "Rare" Vintage Tarot!). Stewart Kaplan has written that he sold 200,000 of them the first year he imported it back in 1960's...and that's what started U.S. Games.