My choice is .btc, though, I'm curious for the reason as to why you'd like to create a new TLD regarding Bitcoin.
I have handful of reasons :
1.Creating a new TLD gives a name standard for all websites whose services is related to bitcoin or the blockchain.
2.The .COM boom has impacted many domains bought only with the purpose of trading them at a higher price later.This raises the initial cost of purchasing a suitable commercial domain.
3.New TLD creates more awareness among the internet users around the globe.