Should I buy disc or download?

[VinylicRook]

Buying CoD4, not sure whether to get the disc or the download, the download is half the price of buying the disc but I'm not sure if it can be re-downloaded when I reformat my PC, I know you can on Steam, but I'm buying from GAME (.co.uk) and it doesn't have any information on there about re-downloading and I want to make sure before buying it, can someone please clear this up for me? and what are the pros and cons for each version, which should I get?

[Shawnibrion]

In a bid to arrest the decline a US consortium of entertainment firms, the Digital Entertainment Content Ecosystem (DECE), has been set up. It wants to transform how consumers buy, access and play digital content.