For daytime travel: a seabird of some sort like a stellar sea eagle or an albatross, cause they have the long distance thing going for them.
For nighttime travel: I'd prefer a bat of some sort but failing that i'd go with an owl
For aquatic travel: I'd like to say collosal squid, but considering all we've ever found of those are bits and pieces stuck on and in sperm whales, i doubt i'd be able to get my hands on one so i'd have to make my way down to the sea of cortez and get my hands on a humbolt's squid cause they're pretty fast and rather ferocious
For self defence: if we're talking animorphs universe here i'd pick a hork-bajir, but failing that i'd go with some sort of tiger
For my own amusement: probably several reptiles like snakes, monitor lizards, and geckoes, as well as a few mammals that might interest me...