Depends on what your definition of "best" is mate. If it's capacity then you have to consider the Maracana for it's atmosphere and sheer size. The Ali Sami Yen on a similar note is one of the most hostile. I like Anfield for it's history. You feel it when you're there. The Shankly and Paisley gates. The Hillsborough Memorial. The Kop. Shankly's statue. This all translates to the stuff legends are made of.
I don't know about best but the Ali Sami Yen, home to Galatasaray houses some of Europe's most fanatic supporters. Coupled with their "welcome to hell" slogan, it makes for one of the most intimidating atmosphere's not just in Europe but anywhere in the world. Many of the world's biggest teams have failed to handle the atmosphere. The only positive point for visiting teams is that they only have to contend with 25,500 delirous fans.
This post has been edited by Duke Red: Oct 5 2010, 04:12 PM
The Maracana in Brazil is one of the oldest of massive stadiums. At one point however is was a decaying mass of concrete but it has since undergone renovations and can now seat 82,000 spectators. In the next 4 years or so they plan to seat 103,000 fans which is bigger than the population of some small countries. South Americans are football crazy and on matchdays it is a cauldron of noise.
Call me ancient but I value stadiums with a great history because feel it's more than just about the facade. A massive stadium is but a tool to create historical moments. Stadiums will come and go but these moments will echo in the halls of eternity.