There are different reasons to use a particular brand/type camera. It could be size, it could be picture quality, it could be weight, it could be several other things. And I'll love to know.
For me, I use a Nikon D750. The Nikon brand was sold out to me as an intern, and I've stuck with the brand ever since; from my first DLSR until now. I've used a D3300, D7100, and now D750.
Before I purchased the D750, I compared it to other models; D800 and D810. But after reading and watching several reviews, I opted for D750. I chose it because of its ability to capture good images in low light. And picture quality was really decent too.
I wanted to purchase a Sony A7rii or A7riii, but I'm not boxed up enough for either of them.
But feel free to share what camera you are using and why?