Which SOC report fits controls that affect a customer's financial reporting?

SOC 1 is the usual fit when the service organization's controls are relevant to user entities' internal control over financial reporting. Think payroll processing, loan servicing, transaction processing, billing, or other outsourced processes that feed customer financial statements.

SOC 2 is not wrong because it is less important; it is wrong when the user need is specifically financial reporting. SOC 2 is built around Trust Services Criteria such as security, availability, processing integrity, confidentiality, and privacy.