I am Gran and my husband is Papa. (It started out as Grandpa, but the oldest grandchild couldn't say that, so she called him Papa and it stuck.) Names on the other side(s) are Grandma and Grandpa, and Grammie and Grampy.
One of my friends is called Lala by her grandchildren and she loves it!
My mother started out as Grandma, then it was Grandma Templeton to distinguish her from my oldest baby's other Grandma. But he couldn't say that, so he started calling her Grandma Tex, since she lived in that state, and she was Grandma Tex thereafter.
All this is to say that whatever you think you like, the grandchild may come up with something else! :^)