How Much Effort is a Pet Worth?

Tropical fish aren't necessarily more difficult than goldfish. It's just that people have long abused goldfish (they really do need good sized tanks, decent filters, and frequent water changes -- really more so than many tropical fish because they eat more and produce more waste).

Humans = fun ∴ Babies = fun. How anyone can have just one baby is beyond me because humans are awesome.

The baby should be much higher on the FUN scale. Sure, for the first three months or so they're not too responsive, but you can pretend they're a puppet and move their arms, legs and talk for them. It's a blast! Plus, that helps them to learn where their body parts are, how to use their muscles and to get familiar with language. And the older they get, the more fun they are.

Plus, there is nothing more fun than lying on a couch with a book and a baby on your chest.

I've had all these except for the Tamagotchi, dragon, and tarantula. I would put babies at more effort than a horse, although they are both outliers. After all, you can sell a horse. But I consider babies more fun than horses -maybe I'm just weird that way.

Another thing to consider with those high-effort pets: the first one is a real hassle, but the second one tends to make things easier (horse, baby, cat, dog). I can't say a second goldfish or iguana makes caring for the first one easier, but there is less capital outlay for the second one. A second hamster or rabbit is real trouble.