There are two competing digital download redemption types, UltraViolet and Digital Copy Plus. Only Digital Copy Plus codes can be redeemed on iTunes. Both codes can be redeemed on Amazon and Google Play but only iTunes allows movie downloads from non-U.S. locations. Amazon and Google Play blocks movie downloads from non-U.S. IP addresses.
A few combo packs contain both types of redemption codes but most that have codes have only one or the other. So, if you're from outside the U.S. the best value combo packs are the ones which have Digital Copy codes that can be redeemed on iTunes, otherwise, you won't be able to use them. Avoid UltraViolet if you can.
Disney only uses Digital Copy Plus codes so you might prefer to wait for the release of Disney's combo packs instead of watching Disney's movies in theaters.