I have only used White Noise, as I didn't really see the need to pay for something like this. I usually turn it on for about half an hour on the Rain setting at around 30% of the volume. My only complaints are that it doesn't save what you set it to. It always opens to waves at around 80% volume, which is definitely too loud to try to sleep by...
And it now costs $0.99, just like the other two.BTW, White Noise was updated yesterday with more sounds and it now saves your settings. Great app!
And it now costs $0.99, just like the other two.
Sleep Sounds is very good. It uses real recordings and has a great mix and match feature so you can create custom sounds based on the existing sounds, so you can create whatever suits you.
http://itunes.apple.com/us/app/sleep-sounds/id390555459?mt=8