Rats, hands down. =D
I've owned mice, guinea pigs, hamster, and most other small rodents, but none even compaire to the compainionship that my rats have given me.
So intelligent, sweet, loving. The one and only drawback is their lifespan, but those 2-3 short years they're with you are the best years ever.. because everyday of those years, they put a smile on your face.
I mean, how can walking in and finding all four boys piled ontop of eachother soundly asleep not make you smile? =)

(And yes, there is four rats there^^)
I could go on forever on how much rats mean to me, but I won't. Anyone who has talked about rats with me has heard it a million times.