A while back we decided to try Sparty's and CKK on the same weekend. Sparty's looked promising - big venue with lots of facilities - but virtually no one turned up. 3-4 couples tops. Very disappointing. The next night we went to CKK. There were 20+ couples in a much smaller, intimate venue, so we've never been back to Sparty's.
We know some people have been to Sparty's and swear by it, but we met another couple recently who said they kept going back there because they couldn't believe how dead it was, but every time was like a replay of our experience. Perhaps some nights are better than others, who knows.
If you're in a couple then we'd definitely recommend CKK. The hosts - Klaus and Lulu - are lovely, and you feel safe and well looked after. The facilities are good, and the whole place has a classy feel. Have met some fantastic couples there, so what's not to like.