NIST 800-53 vs ISO 27001

You should first study information security regulations for financial organizations in the countries you operate to evaluate whether 27001 or NIST is closer to the requirements the requirements you need to fulfill. For example, in most European countries 27001 is more appropriate.

These articles will provide you a further explanation about ISO 27001 and NIST:
- How to identify ISMS requirements of interested parties in ISO 27001 https://advisera.com/27001academy/blog/2017/02/06/how-to-identify-isms-requirements-of-interested-parties-in-iso-27001/
- What is ISO 27001 https://advisera.com/27001academy/what-is-iso-27001/
- The basic logic of ISO 27001: How does information security work? https://advisera.com/27001academy/knowledgebase/the-basic-logic-of-iso-27001-how-does-information-security-work/
- How to use NIST SP 800-53 for the implementation of ISO 27001 controls https://advisera.com/27001academy/blog/2016/05/10/how-to-use-nist-sp-800-53-for-the-implementation-of-iso-27001-controls/