My 2 printers have been getting through a few cooling fans over time. I think I have bought about 3 replacement 30mm fans for my E3D v6's so far. I've also had a couple of bigger fans fail while working in fairly benign conditions, and although the E3D fans get shaken around a bit, they are constantly pulling cool air through so don't get too hot. Now a 60mm fan cooling my Duet board has started to complain when I start the printer, and that one is pushing cool air with no back pressure. The failed fans have had either sleeve bearings or ball bearings, with no apparent difference in reliability.
Starting with the premise that most of this kind of fan comes from China and, in general, they are cheap, nasty and unreliable - what makes a good fan? When I go looking for a new 24v 60mm fan, what should I be looking for?