Only take official White Taxis from FCO. The fare is fixed at €55—confirm this with the driver by asking "Tariffa fissa?" before you leave. Skip the Leonardo Express if you’re tired; instead, take the FL1 regional train to Stazione Trastevere (€8) and then hop on Tram 8 to Arenula/Cairoli. It brings you right to the neighborhood edge without the Termini madness.
Need to hit Termini? Take Bus 40 Express from Corso Vittorio. It’s fast, cheap (€1.50), and way better than the Metro. Just tap your card on the bus.
For granular maps and every way to reach the pad (including the "Smart Commuter" route):