Obviously, the best option is for all parties, including the United States and the EU, to participate and work toward a document acceptable to all sides. The only way to have an effective anti-racism conference is for everyone to be involved. In Durban in 2001, the EU banded together — during the conference itself, after the United States and Israel had already departed — to keep all offensive passages out of the final document. If EU countries are not confident that they could do so this time, then I suppose solidarity is best, but solidarity at the conference would be better.
(image from flickr user Vovchychko under a Creative Commons license)