I guess gold but easier than a gold fish is a , also a fish but more interesting. mice are not that bad and frogs are ok but you need to buy crickets all the time. My hermit crabs always died fast. Small lizards are nice pets but again with crickets. Bearded dragons are good if you like lizards. Fancy rats are nice pets but you need to clean their cages often.
Don't trust any dog/cat answers, if your asking this question then you probably aren't ready to take on a canine or feline. Some easier pets include Crayfish, rats, ants, or mice. A crayfish is probably the second easiest to care for right after ants. They are scavengers and are pretty cool looking, if you don't want them to fight don't get two males or two of the same species. I think it is cool how they fight and if they ever lose a limb they will Regrow it. Try it and of course do research.
VET HERE ! The best answers for this would be Leopard Gecko, and other small lizards. But if your looking for someone to play with, and such, you could get a rabbit or two (two females will NOT fight) I would get two baby males, because they would bond quickly, and they're not as jumpy or scared ! or even a calm senior dog that's just looking for a calm home for his/her last years !