I would probably buy it at a wine shop in the destination of whomever is receiving the gift.

Only time I'd bother with duty free is if the product simply isn't available at the destination. I've bought some unusual single malts at LHR's World of Whiskies for this reason. But the Champagne carried in most duty-free shops is probably main-brand stuff you can find cheaper in a liquor store somewhere.

If there are some truly great wine shops in airports, I haven't personally seen them. Not a Skyteam person so don't spend a lot of time in CDG beyond occasional O&D.