Most fuel efficient Ultra large plane(600+ seats): Airbus A380-800
Most fuel efficient large plane(380-550 seats): Boeing 787-10.
Most fuel efficient medium plane(200-300 seats): Tupolev TU-114
Most fuel efficient smaller plane (100-150 seats): Bombardier CS100/CS300. CS300 has slightly lower CASM than CS100
Most fuel efficient regional turboprop (50-100 seats): Bombardier q400 nextgen
Most fuel efficient regional jet(50-100 seats): Bombardier CRJ-1000
Most fuel efficient plane with <60,000 lease: Cessna Remis F406