I like 'em all.
I prefer Heidi Brühl's version of 100 Mann und ein Befehl to Freddy's--I didn't know of it until Youtube caame along. I also love her 1966 hairdo.
I also like the Dik Diks' version of Sognando la California (California Dreaming).
Il Silenzio by Nino Rosso was a monster hit in Europe in 1965 but did nothing in the US. In fact, I never heard it again after 1965 until I found it on an Internet site in 2000.
And don't forget this one:
Ich Sitze im Schlauchboot (I'm sitting in a dinghy)--Fausti (1969)
Rot Und Schwartz -- Karel Gott.