[@Vilageidiotx] is right; no matter the animal, you have to be able and willing to put in the work. And make sure your pup is going somewhere loving to soften the blow; no matter how poorly behaved they are, losing you is going to be very hard on them.

Now, more to answer your question, have you considered rats? Having owned a small menagerie over the years, I can say that rats are great little buddies. They have their challenges; you need at least two so they don't get bored, finding fancy rats that [i]aren't[/i] sick can be difficult, and their cages need to be big and cleaned frequently. But they're dead clever, loyal, and absolutely sweet. My rats used to sit on my shoulders, climb on my head, nibble my ears and such. If you socialize them from an early age, they're very cuddly. They're adorable, although their little claws are pretty scratchy.