Prices dont vary very much around product launch TBH . Anybody who sell it "cheapest" is your friend
Ive always got it Online ( upgrades ) or local PC World.
Downloads are OK but the price difference makes getting a "hard copy" worth it unless ( like me) the download is an upgrade from earlier version and as such cheaper. Even so, they have the option of still sending a boxed "upgrade" version later on
Later on in the product life , the best thing would be to search online for the keenest deal.
HTH