Across country and overseas: Snap-n-go vs. BJCM

DH and I are going to CA in August and Sicily in September. DD does not have her own seat on any of the flights.

We're thinking about bringing our carseat to CA - especially after reading warnings about rented carseats on this site - but don't know what we're doing in Sicily. BJCM is probably much easier to use when seeing sites in Sicily and we're not renting a car there. We're bringing the Ergo with us and I had been thinking that it's probably easiest to get through airport security with baby in the carrier.

Insights are much appreciated!