All else being equal, you are better off with a smaller dog, of a breed known to be good companions. Why? Because some landlords will have size restrictions or breed restrictions. You might or might not be able to negotiate around those restrictions under disability law, but if there is no need to set yourself up for added stress, then why do it? Dogs under 20 pounds are unlikely to get nearly as much resistance as a German Shepherd, Rottweiler, Doberman, Pit Bull, etc.
Some breeds that tend to make really good companions in my experience include the Boston Terrier and English Toy Spaniel. But there are many others. And don't forget the mixes. I'd go to a shelter or rescue and spend a good amount of time playing with all of the dogs to find the right personality match. And if I didn't find him the first trip, there will be new dogs in a week and you can try again.
A word about puppies. Puppies can suck you in like a black hole. But generally, you are better off getting a young adult dog. Puppies take a lot of extra care. You have to get up in the middle of the night to potty them, if you want them reliably house trained. They chew on things and make messes. They go through several personality changes due to hormones. You can guess what kind of dog they'll be when they grow up, but you won't actually know until they've grown up.
With an adult dog, what you see is what you get. Usually, they're already spayed or neutered. They're up to date on shots and won't need another for a year (whereas puppies need shots every 3 weeks until 4 months old). They've already learned the basics of cohabiting with humans peacefully. Any problems are known up front (if you deal with a good agency). If at all possible, look for one that will let you foster for a couple of weeks or try out a dog. It's a life long commitment, so you want to make sure you two get along really well and are right for each other.