What would be the best audio file atributes for handheld device?

Hello,

We are making a game for iOS and Android. As our focus is primarily on HandHelds and I was wondering what type of Audio file would be best recommend. So If I had to make a list, it would be like

1. File Extension

2. Bit Range

3. Frequency Range.

4. Etc etc etc...

If you have more information or links to garner knowledge regarding Audio Production on mobile devices, that would great to.

Thank you for your help.

ALERT :

I have no prior experience in sound engineering.

• you would have known by now lol**