When I was young and they were alive, I would have said my maternal grandmother was my favorite. But from stories I heard from my mom after I was grown up and all the grandparents were deceased, probably my maternal grandmother would have been the least beloved if I had had the same amount of contact with all of them.
My maternal grandmother was a bit of a hard person, but she baked yummy bread rolls, was the only person who empathized with my shock and terror after being chased out of a field by cows, and was delightfully willing to criticize my parents with me when I was a young teen.
My maternal grandfather died when I was in first grade, I remember him as always sitting down. Also as the giver of nickels to go buy fudgesicles, and for letting me smoke the ends of his cigarettes.
I very rarely had contact with my paternal grandmother, and mostly remember her as being made up of pieces - most frightening experience of my life was having followed her into the bathroom (I was preschool age) and then seeing her take out her teeth (which was as unexpected and outside of my view of the world as if she'd taken off her head). Then some years later it was a shocking disappointment to find out that her adorable silver hair bun was just a clip on! Was there nothing real on this person?! LOL
The last time I saw her was when I was 20 and both grandmothers stayed with me for a couple days to attend my sister's wedding. She seemed like a real nice person to grown-up-me.
My paternal grandfather was a favorite at the beginning of my life, he was very good at swinging me sideways back-and-forth to a Tick-tock-goes-the-clock rhyme that I don't remember now. But by the time I was in kindergarten I found him frustrating, which much later I found out was because he wasn't right in the head since an explosion injury while he was in the army (WWI but not in battle, was helping blow up tree stumps to make a road). I guess the tick-tock rhyme was the top of his mental functioning. But his brothers were all nice, so he'd probably have been a good grandparent sans brain damage.
Sorry this is so long, it was nice thinking about my grandparents.