Whats the best new pet?

I have a ten gallon tank and a hampster cage....I have a fish tank and i have hermit and a dog and i have done tons of pet sitting and i was wondering....what animalshould I put in the tank....i kinda want a mouse but my mother doesnt want me to get anymore "rodents" according to her. What are so ways I could convince her otherwise? and if no what are some other good easier pets i could take care of that only need a teen gallon tank and i am hoping its not to expencive.......thanks for the help!!