Hi Bets,
as a musician I always say what sounds good to YOU is a good sound- for you. Or if you have discovered that certain tones (frequencies) stand out for you, then explore it further (the common keyboards have a fine pitch tuning, for each half tone 10 steps).  But there is so much fine music already canned...
But simple tones/sounds is not the principle of the HemiSync recordings. They use slightly different frequencies for each ear which makes (so they say) the brain respond in a frequency which is the difference between the two original frequencies.

Drumbeats at a special speed also are effective I've heard.

Spooky