The island is pretty small, so you do not need anything massive, a compact hatchback handles those narrow streets way better than a big sedan. Most people rent a car in Malta online before they land, and you can check different ride options and rates on this site
https://getrentacar.com/en-US/malta . Make sure the rental includes full coverage with zero excess, because some local lots lure you in with a dirt cheap base rate, then push pricey insurance add-ons at the counter.