I think
Marco would work best than the others, and it's lovely!
Adán, Andrés, Sebastián i Nicolás are also great! My favourite would be Nicolás, since I adore the nn
Nico.
I also adore
Gabriel, but it would probably be misspronunced.
Anyway, I'd go with a name without accents, it will avoid many problems, I think.
What about:
Paulo or
PabloGuillermo Matías (
Matias) (yes, it has an accent, but I adore it! :-D)
Bruno Hugo (pronunced the Spanish way, OO-goh)
Gustavo (the nn
Gus is cute, imo!)
Leonardo or
Leo (pronunced the Spanish way)
Marcos MauricioNacho -as a full name, or as a nn for Igancio (I prefer the first)
RobertoTadeoMateo Teo
Tristán
Valentín
Hope that helps, and good luck!
EVA