Adopting a dog

I'm seriously thinking about adopting a dog. I've spent a lot of time this week searching for abandoned dogs on the Internet.
I'd rather give a home to an adult dog than buy a puppy. I respect people that prefer a particular breed of dog, but I've seen photos and videos of dogs in animal shelters and they look so sad that I think they deserve to have a family.
My children prefer a female dog, and it should be small, given that we live in a flat.
However, we must think about it carefully, because if we decide to do it, it will be a great responsibility.