Which payment gateway providers offer strong protection and transparency when responding to government data requests?

None. All payment gateways in some manner or the other are regulated by the financial regulator, either directly or indirectly. The home regulator would have the legal basis to look at transactions from a KYC / AML / CFA, etc angle.

Requests from other governments or agencies may be subjected to review and these requests could be denied based on the privacy laws of the land or till such time a court order is issued.