I bought one each of the golfball and the paPst (thank you C'Dale) about two weeks ago and have been running them as case fans.

My impression of the papst is that it's a very high quality fan. The golfball doesn't feel cheap either, but I do worry about its sleeve bearing.

The two fans can get noisy in different situations. The papst will get noisy if I mount it on the front of my case, and the golfball will get noisy if I mount it on the rear of the case, but if I switch them around they seem a lot happier. My best guess is that the mouting positions create different distances between the fan and the honeycomb grilles on the case. The case is an Antec SLK3700BQE with the airflow reversed (exhaust out the front).

Both fans undervolt fine, although my crap vantec controller only drops to 7V.