If you speak a second language better than your native language, would you describe your second language skill as "native" or "fluent"?

This is definitely a bit of a stupid question... but methinks this happens to a good number of immigrants. Asking because there is a bit of a funny philosophical debate here:

• Technically the second language is not "native" by virtue of you not growing up with it
• But you speak it better than your native language, so skill-wise it is "native"

So do you have "native" language skills, or would you consider yourself simply highly "fluent" at the second language?