[name_f]Gianna[/name_f] for sure. I agree with a previous poster that I hear them just slightly differently—[name_f]Gianna[/name_f] with the tiniest hint of a “y” sound, and [name_f]Johnna[/name_f] like [name_m]John[/name_m] + a.
[name_f]Gianna[/name_f] is a lovely name! It’s on my list too 