i would say some sort of mix from a shelter, probably a young dog (not a puppy), possibly a lab or shep mix. also, will you be crating the dog while you're at work? and what time do you leave for work? if you're going to leave at 7 am and not be back til 5pm, get a lizard or a cat or something. a dog needs a lot of attention and time spent with it, especially a young dog.
a young adult dog 2-5, would probably be best, because they won't be as energetic or demanding as a puppy. a dalmation is not a good choice, depending on the individual pit bull, it might be. just be sure you know about the pit bull's temperment before you bring it home. they can be the most sweet, loving, affection dogs, but they can also come from a home of a$$holes and be taught agression.
don't rush out and buy a puppy right away. do your research. go to different breed websites to find out more about them, and look at local shelters. someone there will be able to help match you to a dog.
a great dane might be not be a terrible choice. they're fairly mellow, affectionate, not super-high energy, and of an intimidating size.