I like all three and pronounce each similarly, with a long "i" sound.
I doubt
Gaia will become as popular as
Maia (although I think the
Maya spelling is much more common than Maia)(I prefer the
Maia spelling).
Gaia has the possibility for the "gay" pronunciation, something that makes people here in the U.S. run for the hills. (**rolls eyes**)
Kaia, on the other hand, does have the potential to become as popular as
Maia /
Maya.
Not that you asked, but my favorite combinations for each one would be:
Kaia Liv,
Gaia Helen and
Maia Celeste.