Answer:
I prefer rats myself but the only difference is that mice are smaller than rats. Other than that difference they are exactly alike.
Rats are more social and interactive. They also eat more but smell less. Average lifespan in captivity 3-5 years. Note that rats are very susceptible to cancer.
Mice are smaller and don't like being held as much. They also smell more but you don't have to clean their cages as often and have less needs. Average lifespan in captivity 1-3 years.