I like
Apollo,
Anton,
Severine, and
Tobias best for American babies, although I like
Ari,
Otto,
Rune,
Ulric, and
Viggo anyway, and I have changed my mind about whether it matters if a name "works" in the given culture.
My favorite favorite of the names is
Anton. Kai/Cai strikes me as very trendy for some reason, even though I don't know any Kais or Cais. I think it's partly the spelling and partly the sound of it. Anyway, please please please use
Anton :)