No ethnic group is similar to the Jews. They may be some external likeness, but no one is Chosen but Israel. Now, if you consider Samaritans and Karaites as Gentiles, then these would be considered the most similar. I just consider them as a part of Israel.
Unfortunately Edomites and Ishmaelites, even if enemies, can have a similarity, since Rambam said they were bound to circumcision. But they have chosen evil!!!