My maternal grandfather and paternal grandmother passed away within 2 years of each other when I was 8-10.
My grandmother was someone who I saw often, but I don't honestly have a ton of recollection of interaction with her. She was bipolar(very seriously, to the point where she'd had extended institutionalization over time) and what I remember of her I now mostly recognize as her being medicated enough that she was stable. With that said, even though I don't remember her saying much, my mom in particular talks about how much she liked me and how, despite her limited income, she would have a gift of some sort for me any time we went to see her.
My grandfather I just remember thinking was wonderful. He was quiet but very intelligent and had a very dry sense of humor. I didn't really appreciate that so much when I was that young, but I look fondly back on things now he said to me and "get" them. Later on in life(a few years ago) I got to know his youngest brother, who lived in Wilmington, NC(moved there after medical residency from Central KY, where I grew up), and who I'd never really been around until we went to visit him. After that trip, my uncle(grandfather's brother) and I talked regularly up until he was no longer able to really talk on the phone. My mom said she was amazed that I'd hit it off so well with that particular uncle, since he also was quite reserved(more so than my grandfather) and had to really like someone to even bother carrying on a conversation with them. She said he was a lot like my grandfather(who had 7 brothers, and of course with a wide spectrum of personalities) and my uncle and I both expressed some regret that it wasn't until I was in my 20s and he was close to the end of his life before we really did know each other.
My other two grandparents were a bit of a different story. I lost them both in 2014, and within a month of each other.
My paternal grandfather lived in the mountains of North Carolina in a little town in the northwest corner of the state that he'd just happened up and decided to buy a house there. We would visit for a week once a year or so, and as he got up in years he started wintering in Kentucky and then moved back full time. Even though I was around him a lot and knew him well, he was someone who was hard to really get close to. He gave my dad a real run for his money when he did move back here. He and my dad honestly hadn't had the best relationship growing up, and there was a lot underlying that. Still, though, I'm glad to have known him, and I can hear him in my dad quite often. My MKZ that I still drive belonged to my grandfather, and I bought it from him when he decided to hang up the keys(about a year later than he should have). When he turned 90, he went down to the dealership in town and said "I'm turning 90 and I want a new Lincoln."
My maternal grandmother was someone I was very close to. I stayed at her house often(especially when I started graduate school and she was closer than my parents) and would often travel with us. We had a lot of good times with her, and she was sort of a constant presence. She had her own way about her, and things she did that would aggravate everyone that we look back on fondly now. Still, though, I think of all of my grandparents, her passing hit me the hardest. It was also partially too that she'd seemed virtually invincible and immortal up until the last year of her life, when she was finally diagnosed with ALS and we watched her slowly slip away. As my mom has gotten older, she reminds me so much of her, to the point that sometimes my mom will say things and I'll call her by my grandmother's first name.