Always NaNO2 (Sodium Nitrite)... Never use sodium azide (NaN3).
Sodium azide is not in any way peaceful, it also can explode if it comes into contact with certain metals (causing it to form hydrogen azide).
The only advantage sodium azide may have (depending on the situation) is that sodium azide has no cure. So once you take it, there is no saving you.
Whereas sodium nitrite poisoning can be reversed with the use of methylene blue.