I called both of my grandmothers Nana. I hadn’t given a lot of thought to what I would be called but a friend of mine (younger than I) chose to be Grandma, which I think sounds older. I shall be Nana when the time comes.
Grandma last name. both maternal and paternal.
“Grandmother” is “Nonna”. “Nonni” would usually be grandparents.
My grandparents were grandma and grandpa , first names added if necessary because my parents apparently had issues with using non-English words- all my friends used the English words at most for one set .The other set was nonna and nonno or oma and opa ,etc
My kids call my mother “nanny”* and called my father “grandpa”. My husband’s family, it’s grandma/grandpa last name.
*I have no idea why my nephew called her that, but he’s the oldest and all the rest followed
Grandmother on my father’s side was ‘Granny’. Grandmother on my mother’s side was “Gabba.” Both sadly passed and not able to hear us any more. 
Both of my grandmothers were Grandma, pronounced more like Gramma. My maternal grandmother was called Mammy by the rest of the family. My in-laws are/were Mimi and Pop. My stepmother and dad are Mamaw and Papaw to her grandkids, and he is Grandpa to his. My sister-in-law is a Grammy.
Here in Kentucky, there are a lot of Meemaws, Mamaws, and Papaws.
Paternal grandparents were MawMaw and PawPaw. Maternal grandparents were Papa and Grandmother. My kids have Granny, Granddaddy, and Nana. We’re from Alabama, for what it’s worth.
Paternal: Grandma Beitz
Maternal: Grandmama, but when we got older it morphed into just “Ma”.
My kids refered to my Mother as Grandma first name, and to my wifes Mother as Nana.
My Grandchildren call my wife “Nanna”
What, no snicker afterwards? 
Oma, she was from Germany.
My mom was half Cuban and I was raised in Florida. Abuela is what we called her mom.
Dads mom was already dead before I was born.
My mother’s mother was “Grandma.” My father’s mother was “Grandmother.”
As you might guess, my father’s mother was not the warmest person who ever had grandchildren. I once asked my older sister (the oldest of all the grandchildren) how it was we all came to address her so formally. “I think we all just understood that’s how she wanted to be addressed.”
I had a Grosie (how she signed cards) too! She was Pennsylvania Dutch and grew up in Indiana. My grandmother from Tennessee was Granny.
Mine were the fairly mundane “Grandmother” and “Grandfather”. Those were my mom’s parents, Grandmother was from Alabama, Grandfather was born in Washington state.
The other grandparents lived far away, and died anyway before I was very old. Never really had the chance to call them much of anything, though they were occasionally referred to as Grandma and Grandpa (Lastname).
My own kids have “Grammy and Grampy” (my parents) and “Mimi and Pappy” (husband’s parents).
One of my kids had a hard time saying Grammy, so he called my mom “My 'Ammy” and she liked it so much that she wishes they would all call her that.
This is Texas though, so I hear a lot of the MeeMaw and PeePaw, MawMaw and PawPaw, and other more odd ones like “Sissy” and “Nanny” for grandmother, and PopPop and GramGram for grandfather. Especially with your more rural people - the grandparent names just get stranger and stranger. (To me, at least!)
My grandmothers were Grandma Lastname, so Grandma Smith rather than Grandma Mary. Same with my grandfathers.
Somewhat bizarrely, “Grandma A” and “Grandma B”.
It was because of the first letters of their lastnames, but in retrospect, it does seem kinda like the impersonal naming scheme you’d use for people in a police lineup, rather then nicknames for close relatives.
Dead.
Otherwise, my paternal grandmother was always referred to as “Grandmother [last name].” She died when I was eight, had lived half a continent away in California, and I had only one shadowy recollection of ever meeting her once when I was much younger.
I was rather close to my maternal grandmother. She lived in Arkansas, I saw her once or more a year while growing up in West Texas – we even lived in Arkansas not too far away from her for a few years before settling in Texas – and still pretty often as a young adult, and she did not die until I was in my 30s. She was always called Memo*****, which was apparently my futile attempt to pronounce “grandma” as a very young child. The name just stuck.
I think the more formal designation for my paternal grandmother was due to the lack of familiarity with her.
*****Pronounced “MEE-mo,” not “memo” as in “memorandum.”
Since this is a poll, moved to IMHO (from MPSIMS).
Nann and Grandad on my fathers side.
Mum’s mum died when I was 1, and her dad wouldn’t be called anything except his first name.
My dead grandmother was “mormor”, which I guess she got from her grandparents, who were Swedish immigrants, and my live grandmother is “grandma” or “grandma firstname”. My great-grandmothers were both “grandma lastname”. We’re all from CA.
My German grandparents were Oma and Opa, and when my mom became a grandparent, she was Omi.
My Mississippi grandparents were Granny (last name) and grandpa (last name).
My husband is from West Tennessee, and his are Meme and Papa, and Ma (last name) and Pa (last name). Very small town southern.