I have watched some videos on YouTube about the strength of evidence of some documents. I'd say that affidavits involve people, which is good, because it shows other sources beyond yourself willing to vouch for the marriage. Keep it diverse (like, not just two people who are married to each other and are vouching as friends, better add more individuals outside of that) and keep it simple and not a whole page or story.
Now regarding RFE's in general:
Some evidence is very flimsy, like shared bills for Spotify or a phone bill. Many people can get a bill together, not necessarily married people. Many people are on the bill for a utility, or even a rent agreement.
Solid evidence:
- Filing taxes together (DO NOT SEND TAX FORMS, go into IRS.gov, make an account and pull the TRANSCRIPTS for all years filed together)
- Having children together
- Having each other as beneficiaries for insurance, 401k (or 403b, ROTH IRA, etc.) and such
- Sharing insurance for cars, residential (renters or homeowners)
- Having shared investment account
- Property (home, car titles)
All of these carry a level of mutual long term financial risk that affirm the marriage is bonafide. I would push more in that direction if I had an RFE.
Good luck.