Aaah, I don't knowww-
They're both great.
Karen Fukuhara also voiced Kipo in Kipo and the Age of Wonderbeasts (which is such a good show).
And Vella Lovell also played a character a lot like Mermista on the show Crazy Ex-Girlfriend. (I haven't watched it, but I've seen clips of her in it and she's very funny. This song in particular.) This is apparently part of how she got the role as Mermista. (source)