Why would you ever choose something else if the regrab is guaranteed? Fair and uair could be DI'd and you'd have to react, while a regrab will reset your initial position. Just keep chaining the grabs together until around 55%, at which point you can get a tipper fsmash really easily on hard lateral DI (and lesser opponents will usually keep DI-ing away, making it an easy kill). At percents past the window for regrabs, uair should work and should be fairly easy up to high percents.
This being said, there are times you can't get regrabs, like if you mix platforms into the equation in which case it's worth looking at alternatives. But when it comes to chaingrabs, the next grab is always the most important thing unless you can secure the kill with an attack.