I like Jax, but only as a nickname. It's charming and playful, and it's a nice alternative for Jack. Charlie Hunnam plays Jackson "Jax" in Sons of Anarchy, and the more I watch that show, the more I like the name Jax... :)
This must be why my sister likes the name. She told me she likes Jax as a nickname for Jackson (Luckily, not Jaxon) and she watches Sons of Anarchy. I've never seen it though.