Considering both are a $1, I can hardly complain.
I recently bought Ambiance and a Sony docking Alarm Clock just for it.
The sounds seem basic. Ocean didn't thrill me, too hard on white noise than soothing. The fan and machine are nice and different from sound machines I've had. Rain, simple, but good. Creek, sounds good, but haven't used it, with like something a little slower and suddle. Waterfall, sounds like a big one.
One annoyance is all the different white noises, like Pink Noise, Violent Noise, etc, that are scattered throughout. So if you want to browse the sounds while play, they are pretty startling.
Though, update doubles the amount of sounds and haven't tried it yet. But for the cost, buying both apps would be a no brainer.
Also, there's this 3rd app that just came out. But until Apple releases their 1.1 update, the sounds have a noticeable hick-up when they repeat.
http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=288353538&mt=8