I must say that I like Linkin Park, but I'm not a huge fanatic and I don't think I would call them the biggest rock band just yet. Honestly I really don't know who would be called the "biggest" rock band. There are too many successful bands to tell right now. For all we know Alter Bridge may be the next biggest band.
Even though Creed is over with, they will always be the biggest rock band to me because of the way their music touched so many people's lives.