Tokenization is the appropriate method to secure sensitive data at rest, especially for financial transaction data which can contain credit card numbers or personal identification information. By replacing sensitive data with non-sensitive placeholders, tokenization allows the company to handle payment information without exposing actual sensitive data, thus maintaining compliance with industry regulations like PCI DSS. On the other hand, masking and obfuscation may hide data but still could leave it vulnerable to unauthorized access, and hashing, while useful for integrity checks, is not reversible and thus not suitable for data that needs to be retrieved in its original form.