On U.D.O.'s official site, there is the following announcement :

"U.D.O. will do a "Best of" - album which will be released on December 7th and everybody has the chance to contribute at the song selection there, with the album really deserves the title "best of".

To take part is very easy: send an email with maximum 3 titles to best-of@udo-online.de.
Deadline for the voting is September 15th and there is only one vote per person allowed!

You can trace the continuous updated score of the voting on the website in short."