depends which airports you're going to really - probably a bit cheaper in paris airports.
if you have an afternoon or morning to spare when in dlp, i would try going to the shopping mall at val d'europe. they have a sephora there which does really good perfume - i got a bottle of their own brand for 18euros, 100mils, and it is 'vanille chocolat', and they have around 12 of these vanille scented perfumes mixed in with another scent - the one i have smells remarkably like thierry mugler's angel, but for a fifth of the price!
but yes, would probably go with paris airports, not much of a saving, but probably a better range in cdg or orly.