Do 2 Silver until you unlock most of the uncommons.
Basically, and this goes for everyone getting REQ, this is the best choice. I mean, you've got Common, Uncommon, Rare, Ultra Rare and Legendary cards.
Bronze only has Commons
Silver has Commons to Rares with 2 guaranteed permanent unlocks.
Gold has Uncommons to Legendaries with 2 guaranteed permanent unlocks.
As a few people have explained, unless you are somehow guaranteed to get at least a single Ultra Rare, there is no reason to get a Gold REQ, since they're still heavily weighted towards Uncommon cards. You could blow 10,000 REQ points and get 2 Uncommons or you could blow 10,000 REQ points and get 4 Uncommons.
There's the miniscule chance that you'll get an Ultra Rare or Legendary, but after like 7 Gold REQs I've gotten exactly 1. You're better off using Silver REQs to unlock all of the Commons and Uncommons and potentially get a few Rare cards, and when you've gotten most of them you can shoot for Gold because it's more likely that you'll get something rarer (seeing as you'll get 2 permanent unlocks and no permanent unlock is unlocked twice).