Uhm, new blood and extended are the most rewarding packs
new blood pack value depends on the current new blood cards.
you can save your credits and buy many new blood packs when a expensive card is released (every 2 weeks on friday new cards are released) or you can just take the clans urdb says to take and buy extended packs
if you want specific clans and cards not to sell but to keep, you can try elite
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