Balthazar is a very neat name! I think with
Sebastian it's a bit overkill, because they are quite similar in style (long, impressive, somewhat European).
I prefer
Balthazar, just because I think that's the spelling most people would leap to. However, it's such a showy name that it doesn't really need the Z, so I love
Balthasar too.
I like..
Balthazar MiguelBalthazar DiegoBalthazar NicholasBalthazar JesseBalthazar JayBalthazar AntonioBalthazar ManuelBalthazar FrancisBalthazar PeterBalthazar Teague
Something a bit plain/common/normal works best, I think.