I called my maternal grandmother "Gram" most of the time. My paternal grandmother was a little more formal; she preferred to be called "Grandma {lastname}.
My mom goes by "Oma" and my dad (while he was alive) was "Opa" to my niece and nephew. I like that, it's easy for little ones to say. They call me "Auntie Blue" (my family nickname is "Blue") but when they were younger it came out "Annie Boo", which I loved! They're 11 and 8 now and I miss being "Annie Boo". "Auntie Blue" is pretty cool too, though.
