If Pokémon were real... I'd go for Venusaur. I could ride it (granted, I could walk faster), it has Sleep Powder to help me go to sleep, it's beautiful (in a manner of speaking)...
Charizard would be neat to fly with, but too "hot"-headed :) Then the others aren't big enough/I wouldn't want to ride on.
Wait, others brought up good points... I wouldn't have to evolve it! Maybe Ivysaur still... Chimchar is cute, but I don't like monkeys. Charmander seems lovable, as does Squirtle. Piplup, and Chikorita would be good too. Oo, Meganium! Ehem... that sounded flamboyant :) Probably Chikorita though, it's adorable!