quietest coolers available?

It depends on the cpu, whether it's stock or overclocked, how much heat you're trying to get rid of and how much money you're looking to spend along with how big your case is.

If you're running a locked i3 or a stock i5, the h5 is probably fine. If you're running a heavily overclocked i5 or i7 you may want something different. In terms of air coolers it depends on what case you've got, if the case is too narrow then a cooler that's too tall won't work. Ie a case that only supports coolers up to 155mm a 160mm cooler is unlikely to fit.

Is it a windowed case and how important are looks? Some decent coolers out there like the reeven justice are fairly inexpensive compared to say a noctua nh-d14 but it's got a rather bright yellow fan. If yellow isn't your thing then it could look awful. If you don't like noctua's brown earth tone colored fans there are others out there like the cryorig r1 universal, bequiet dark rock pro 3 etc. Those are more in the $65-85 range where the h5 and reeven justice are more in the $45 range.

Is there a big difference? It depends. At low speed (7.5v) there's not a huge difference, something like the dark rock pro3 runs at 25dba and cryorig h5 runs at 29dba. At full speed (12v) the dark rock pro3 can go up to 39dba while the h5 will get up to 53dba. That's pretty significant, every 10dba the sound pressure/noise effectively doubles. 50dba will generally be a lot louder than 40dba.

If you're running a cpu that runs hot like an oc'd i7 4c/8t or 6c/12t etc then an h5 is going to have to work harder than a larger cooler like the nh-d14 or dark rock pro 3. If you're running a cooler stock cpu the h5 may not get up to full speed or won't be at full speed (noisy) as often. A larger cooler like the dark rock pro 3 which is what I'm using on my oc'd 4690k never reaches full speed. Meaning due to being larger, not only is it's top speed quieter than the h5 it's quieter yet because it never has to work that hard. It maybe runs at 50% fan speed at most even while running intensive programs or gaming.

In order to get my cooler to spin up to max I had to run prime95 with the cpu overclocked to 4.6ghz and turn off all my case fans which is a worst case scenario. Right this minute I feel it's overpriced at $83, it's a much better buy when it's closer to $65. Prices tend to fluctuate. I'm happy with the performance and looks of it with a windowed case, my ram is short enough that clearance isn't a problem, my case is wide enough to accommodate it and luckily I got it on sale. At $83 I'd probably look for a different cooler.

Some of these circumstances may or may not apply but they're all considerations when picking a cooler. Larger coolers don't have to work as hard and therefor stay quieter than smaller ones do. Case size, ram clearance, ambient temps, case airflow and so on can all play into it as well as looks and price. Hard to say though or make any real recommendations without knowing more about what you're cooling.