As far as I've learned of things like Ark and Spark (which uses a statechain), it seems unlikely that they would be good at serving darknet markets. Ark and statechains have to bridge to bitcoin mainnet and those bridges seem like they would be very easy to blacklist. If there is a particular Ark or Spark entity that becomes known for serving darknet markets, I could see exchanges and regulators putting a lot of pressure on whatever UTXOs are the bridges to mainnet.

I don't know enough about Citrea and Alpen to say whether they could be censorship resistant. It certainly seems to be the case that Citrea is going full kyc for their stablecoin. I'm unclear what they will require for using bitcoin in their ecosystem, but I doubt they'd resist kyc-ing everyone.

My money's still on lightning. It's probably got the best shot of being a useful payment layer for darknet markets.