Pitbulls are great dogs. But like any other dog, you need to get one that is a puppy so that it can be properly trained and be trained to live and get along with a small dog. I would not get a pitbull from a shelter, it is waaaayyy too risky. You need to get one from a reputable breeder. Also, make sure you get to see both the parents, you want ones with great dispositions.
Any dog can be trained as puppy to be kind and gentle around small dogs. I have always owned big dogs and small dogs at the same time. I have always got them all as puppies and raised and trained them the right way. My dogs knew that the had to be extra gentle and careful with a small dog. They would even look down while they are walking to make sure they don't accidentally step on them. So big dogs and small dogs can live together peacefully. Any big dog breed can be trained this way, it is just important to get them as puppies and really be on top of the training.
Like I said pitbulls are great dogs just like any other dog. Unfortunately they have gotten a horrible false reputation. Anydog can be aggressive and mean, it has nothing to do with the breed, it has to do with the up raising and training of the dog. I have seen even golden retrievers be really aggressive, and they are one of the sweetest dog breeds.
So as long as you get a pitbull puppy, are willing to do the training and will be dedicated to the training, then I say go for it!!!