SetVertexDeclaration or SetFVF?

SetFVF() is the old way and SetVertexDeclaration() is the new way. The latter can do all of the first but not vice versa. Using vertex declarations you can control more directly how your vertices are built up and, most importantly, interpreted by shaders.

Greetz,

Illco

What is new about it? What advantages does it have?

With a vertex decl, you can completely control:
* The order in which parts of your vertex are laid out
* The streams that each part of the vertex should be taken from
* The data format of each part of the vertex (useful for compressing vertex structures down)

FVF codes, by comparison, require each piece of information to be a specific type, and requires them in a particular order. And to the best of my knowledge, will only let you sample from stream 0.