Would a betta fish like an airstone?

No Kitty they prefer calm, still waters with no current. The addition to an airstone could stress the fish.

Goldyfan is correct. they prefer stiller waters. However some bettas will tolerate a little current as for in fliter flow. Bettas do not need the water airated. they do not breathe through their gills pr take air from the water. Bettas have a laybrinth organ and they go to the water surface to get gulps of air to breathe. If you watch a betta for any amount of time you will notice he goes to the water surface frequently to get breaths of air.

Oh I didnt know that...

I'm glad I found this thread, I had an airstone going in my betta tank up until about 30 seconds ago!