I bought a ton of fans to compare with and my experience is like most - I order them hoping for rainbows and unicorns, only to watch the temperatures rise to basically unusable levels.  The only real alternative I've found is this, the Ultra Kaze:

http://www.amazon.com/gp/product/B001JKNMBE?tag=ana024-20

It's not a silent fan, but it's much quieter than the stock fan... Although I will say that with the new firmware, set to manual speed about 30%, then it's much closer (I still prefer the Kaze).  The big downside with the Kaze is that it's a 3-pin connector, so no PWM control - but the upside is that it's cheap, especially compared to some of the other fans out there.

I did a bunch of tests of different fan configurations, and they generally don't make as much difference as you'd think - if anything, they do more to alter the temp sensor on the board than anything else.  My top 3 biggest improvements (in order of impact) are; fully enclose w/ fan spacer, kaze fan (pull), headsinks on all copper pads.  I've done it on almost all of my S5's, and in general I see a temp drop of about 10c over stock.