I prefer Mira. Aya isn't bad, but I think Mira is a more "solid", timeless name. Aya seems a bit more trendy.
Quite surprised that pps are linking Mira with Myra. They're two different names with different origins, and they're pronounced differently. It wouldn't occur to me that anyone would pronounce the letter I in Mira like the letter Y in Myra. Just like you wouldn't pronounce the currency Lira like the name Lyra.