Bitcoin and Monero, Monero preferred.
TorZon accepts two coins, and the choice is simple.
Monero is the default and the right choice if privacy is the reason you are on Tor, because it hides the sender, receiver and amount. Bitcoin sits in the list for the vendors who only take Bitcoin. Deposit addresses are fresh per request and never reused.
Default to Monero unless a vendor forces Bitcoin. If you pay in Bitcoin, do not send straight from an identity-checked exchange, because that ties your name to the deposit. Route through a fresh wallet or swap into Monero first.