I have yet to use watebased paints, but AutoAir is the BIG thing now with a lot of airbrush artists...my friend uses only that and he is wicked good. Non toxic is a plus but they have insane colors and since you have'nt really started, you'll be fine with a new product. Nitro is so old school, it's yellows, cracks...it's a relic's dream but for custom art, go with this and use a poly clear (catalyzed) for max gloss and depth. Good luck.
http://www.airheadairbrush.com/createx_auto_air.htm