Unlimited Booster packs came with sixteen cards (one more than the Limited edition set). The additional card was an extra Rare card. Also, unlike the Limited edition set, there is a chance (approximately 1 in 24) to get an Illuminati card in a booster pack.
This is the edition to look for if you are planning to play the game, since significant wording changes were made between the Limited and Unlimited printings.
The backs of the cards of the Unlimited set are the same as the backs to the Limited set, so they can be used interchangeably. The titling of the cards is different so they can be distinguished.
There was a total of 409 cards: 100 Rare, 100 Uncommon, and 200 Common, and 9 Illuminati. 200 of the cards were Groups/Resources, and 200 were Plots.