Here's my assessment:
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Ferrets are fun, high-energy "stinky slinkies". They require all those mammalian things like frequent food and water and space and toys and companionship. They need fairly active babysitting if you're away from home for more than a weekend.
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Parakeets are the most delicate creature here. They can't be handled like the others and need a perch and cuttlebone, some temperature control, and even good quality air.
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Pigs are smart and though I'd love a little beer buddy, as others have said they never stay little. Older pigs can need a lot of space and simulation and companionship or they can become very irritable and destructive.
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Bearded dragons are pretty easy going and great pets. Like any lizard they need good temperature control but otherwise they don't require a ton of space and not nearly as frequent food and stimulation as a mammal. But they're easier to interact with and less delicate than birds. Clear winner.
For those who like this topic, check out Clint's Reptiles on YouTube. He's a biologist with episodes on "Is X the best pet for you?" and has already covered all of these (as well as far more exotic things like spiders and cobras).