Sharpies are a wonderful breed, bred for loyality, trains easy, very smart and funny too. meduim size dog, i have 6 and each one has a different personality.
MROSE, not sure where you live (obviously in some US states u may not be able to have the dog im about to suggest.) but I'd suggest a Staffordshire Bull Terrier, not the Amstaff, as they are larger, female staffies dont grow to be massive (14-16"), will live fine within an apartment or small house. My staff gets on fantasticlly with all other animals, and would make an impressive looking guard dog! Check out this link... http://puppydogweb.com/caninebreeds/stafbullter.htm