I’d pick the First Growth so I could post a tasting note about how great the Chateau is, even in ‘off years.’
Generally speaking my preference would favor drinking the weaker vintage GV (‘04 or ‘07 Montrose (but just not the ‘13)) over the better vintage 2nd wine (‘09 or ‘10 Dame de Montrose), but in 5 years time once that ‘09 or ‘10 2nd wine softens and starts developing its secondary nuances, this would undoubtedly make for a much more interesting discussion.
Agree with Gerard. It depends.
I would take almost any second wine from a good vintage over a 2013 grand vin if forced to choose. I’d likely take neither. There might be some grand vins from 2004 or 2007 that I’d take over some seconds. Would depend on the price.
The issue for me is accessibility. That 13 Montrose won’t be even decent for awhile, even with long decants. The 15 Dame is fantastic atm, and even the 10 is drinking pretty well with a bit of air. I tried a 14 Montrose lately with 2-12 hours of air and it was an impenetrable wall of tannin. It opened up on day 3-4 of being open, if I recall correctly.