Sunon HA3010V3-0004-A99 (maglev bearing, 17.6 dBa), Digikey 259-1615
Nidec/Copal F310R-12LLC (sleeve bearing, 13 dBa), Digikey 563-1127
Both are 30mm square by 10mm thick and move around 3 cfm of air.
Both are also 12 volt fans, yet another issue when selecting 30mm fans (a lack of 24 volt options).
I already have an adjustable step-down regulator that supplies the hot end fan, so that isn't such an issue on my particular printer.
As I had mentioned earlier I generally don't care for sleeve bearing fans, but with the Nidec's ultra low noise level I just couldn't resist trying one.
I have had some experience with maglev bearing fans and they have been OK, however I have only used them in stationary applications, not at the end of a rapidly accelerating printer hot end.
So between the two, who knows what will happen?
Hopefully I will receive them today or tomorrow.
UPDATE- I received them today.
They are both extremely quiet and move a decent amount of air.
Of the two I already prefer the Sunon HA3010V3-0004-A99 because although marginally noisier it also moves noticeably more air.
I did not have time to actually install and run it on the printer but I will in a day or two.
I am mainly concerned as to if it moves enough air to keep the E3D heat sink cool.
However, I can say for certain that either of them are far quieter than the one that is on it at present (a night and day difference).