How to make sounds as small as possible?

[William de Smet]

Hi there,
I use spoken words and sentences in one of my apps.
There will be a lot of these so I am probably talking about a lot of MB.
I use Quicktime Pro on my Mac to record and edit them.
When exporting them I get a lot of choices and I noticed the size and sound
difference on 16 bit, 8 bit, stereo, mono, aiff, wav

What is the best way to do this?

Thanks!

William