Rome has two airports on opposite sides of the city, so the first thing to check is which one you're flying from. Fiumicino Leonardo da Vinci (FCO) is the main international hub, 30 km southwest, home to ITA Airways and the intercontinental routes. Ciampino (CIA) is the smaller budget airport, 15 km southeast, mostly Ryanair and other low-cost carriers. Hotels near either Rome airport are the practical choice for a very early departure or a late arrival, sparing you the long transfer into the city.
The Leonardo Express links Fiumicino to Roma Termini in 32 minutes; from Ciampino, shuttle buses reach Termini in about 40.