Visited Frankfurt in 2006 & 2005. Hit Palace which is in town, Oase a bit far out, Malibu (niche club also far out) and World (way far out)

Palace is my favorite, although Oase had the most girls. My experience even at different clubs was similar, rules and on again off again performance. I had some great session but most were too mechanical.

The Terma scene in Rio is much better, almost all girls give it their all. Those are the places I would return to (not likely though) but I think everybody should visit FKKs the sheer number of naked 1st world girls is something you won't see elsewhere.