You would prefer a capped note if you think you'll raise at lower caps. If you think you'll raise at a $10m post-money cap then a SAFE with a $20m cap is better than an MFN SAFE

I don't understand. When would a company ever want a capped note? It only provides a benefit to an investor, at the company's expense.

with MFN clause, it is capped to your next SAFE cap. YC probably expects most of the companies to raise a SAFE round after YC.

No reason to prefer the capped, but I definitely might prefer to not take the note at all.