Skyblock.net is a more survival server with grass diamonds iron as the money, but Skyblock.org is a more economy with money ((/bal)).
The .Net server is based on a survival experience, using Diamonds, Grass, Spawners and all those rares as the currency, it is an economy server so players make up what things are worth what. The .Org server is based on money, not in real life money, but ingame money as in $. There are set rates for what you buy and it isn't as Vanilla as .Net is. Hope this answers your question
.net is more about survival, and you trade with items such iron, grass, diamonds, spawners, and rares. .org has more of an economy, and you trade with in-game money.