An interesting question. I like the Reserva D'Chateau the best however, the "best" Opus X depends on what you're in the mood for at the time. If you're in the mood for a STRONG Opus X, then go with the Perfecxion #4 or #5. If you want to smoke an Opus X BUT you're not in the mood for one that will knock you on your butt, then smoke one of the bigger ones like a Reserva D'Chateau or a Double Corona.

The Fuente Fuente is also a good one but fairly strong. I don't like the xXx aka "Power Rangers" or the Belicosos.

The "A" is a very nice, milder Opus X which smokes very nicely. Those are a special treat BUT they are probably the mildest of the whole line.