Nia is pronounced NEE-a.
Naia is NAH-ya.
Nyah looks trendy and made up and like it is supposed to be NY-a.
I like
Naia and
Nia is okay. I dislike
Nyah. It just looks horribly misspelled to me. Same with Myah and Kyah, they are pretty much the worst spellings I could come up with for these names.
Even Naiya is better.