If you discount the regions where government puppets were installed (E.g. Vichy france, Ustacha Croatia, etc.) it would probably be either the Baltics region or Ukraine. Both were bound together by their hatred of the Soviet Union/ Russia and both had a pretty deep running antisemitism.

In Latvia you have antisemitic pogroms, and many Ukrainians were put into foreign SS-Divisions. Even though this wasn't always voluntary and especially later on there was a forced draft for these troops.

But especially in the beginning of the eastern War, many Ukrainains were hoping for freedom from the Soviets through Nazi Germany. This thought turned over with time, when they saw that the Nazi occupation was even worse. A key figure here would be Stepan Bandera, who's role is even important to this day.

An interesting thing is that during the battle for Berlin most of the SS divisions were made up of foreign troops. They had to fight to the end, because they knew when they come home they will be tried for high treason and most probably sentenced to death.

One disclaimer, the collaboration always pertains to certain people, not all of the people in a given country. It's not like Ukrainian people supported the Nazis wholeheartidly and unanimously. There, of course, also was resistance.