Should I have a puppy or a dog as a college student? ?

I am 21, been in college 3 years. I live with 2 roommates & a maltese 1 year old. I am thinking about a yorkie 1-3 year old. I looked at ownership costs monthly v. yearly. I take 3 classes a semester & work part-time. I love being active & hanging with a maltese, seeing my roommate take care of him (health, heartworm pills, etc) helped me learn. I think the maltese would have someone to play with when we're not home & I wouldn't be so depressed when I'm home alone. Do you think i'm ready to take care of a dog, and can handle the time needed to devote?