Best / worst interest day-count convention for borrower / lender.

Which interest day-count convention is considered the best or worst for money borrowers and lenders?

For example, how do I know if 30/360 is better than 30/actual ?

The best interest day-count convetion for borrowers are the worst interest day-count convention for lenders.

Interest day-count convention has impact on Interest amount.
The formula is:

Intetest Amount = Principal × Basic interest rate × Day-count convention

For Borrowers, the best interest day-count conventions are 30/365 or Actual/365. It is because dividing the annual rate by a 365-day year results in a lower daily interest charge.

For Lenders, the best interest day-count conventions are Actual/360 or 30/360.

Example of 30/365 calculation:
Principal (Loan amount) = 10,000 USD
Annual interest rate = 5% = 0.05
Time period = 30 days
Daily rate = 5% / 365 = 0.0137%
Intetest for 30 days = 10,000 USD × 0.0137% × 30 days = 41.10 USD

Example of 30/360 calculation:
Principal (Loan amount) = 10,000 USD
Annual interest rate = 5% = 0.05
Time period = 30 days
Daily rate = 5% / 360 = 0.0139%
Interest for 30 days = 10,000 USD × 0.0139% × 30 days = 41.70 USD