>>35179106Probably Tropius.
It's easy to care for, mostly just needing sunlight and water. It's large enough to conceivably actually transport a human, and it's an endless supply of fruit.
Other options:
Misdreavus. Cute ghost pal that doesn't seem to have anything innately hazardous about it. Cheap (Free?) to take care of, can do some fun, incorporeal shenanigans. I get to do research on it.
Chansey/Blissey: Super good to squeeze, produces eggs that actively make you happier, and will go out of its way to look after you. Might eat a lot though, and who knows what kinds of nutrients it needs to distill happiness. People will hassle you to get those eggs. You might get uncomfortable when you realize that your Chansey wants you to eat all the eggs.
Audino: Similar to Chansey, though without the eggs, and potentially tricky upkeep. It does have better formed hands, and a good sense of hearing that might make it a better security asset.