more fans = more noise....
Eheim as they said above... just got a 1262 for my skimmer and its silent compared to the sen, heck its silent compared to my mag3 and mag 5's.
noticeably less heat than the sen900
granted mag9.5 isn't a sen.
The qo4000 is a joke up against the eheim1262. qo4000 is a lot cheaper than any of them, fairly quiet as well and energy efficient, have to loosen pump input to keep from having restart problem. At least this is how i cured the problem on mine.
while the qo4000 flows over 1000 gph without restriction, the eheim full bore is 848gph, put 6' of head on it though and the stories are reversed, eheim kills it in flow and every bit as silent.
Eheim is worth the extra 56% more money over a mag9.5.
IF you argue reliability, mag is better than quiet one, but eheim is that much better than either...
mags not unheard of to go 5 years. i've heard eheims going 40 years and still running, by a vendor that is been in business that long... yes eheims will break, but what breaks is the rod/impellor, if you replace $2.00 rod every couple years it'll last without breaking pricey impellor.