Adopting an animal

Live on my own since the girlfriend moved out a couple weeks ago, had a cat that I loved to death for over a year but I found out a few months ago she had feline leukemia and it was getting bad so I made the hard decision to put her down. I feel I've taken my time and I'm ready for a new pet, I love cats and dogs. Cat and dog owners, what are the positives and negatives of said animal? I am kinda wanting to get a dog since I could actually take it outside but I live in a smaller apartment so I'm not sure if it's okay with not a lot of space and not getting out much with me working. Obviously cat is pretty self sufficient more than a dog with smaller space but what are your thoughts?