Which credit score is most important?

There is no right answer to this question because lenders use multiple credit scores and scoring models. Additionally, there are different versions of these credit scoring models. The best answer would be to check the score and scoring model your lender may use. 90% of credit card companies and lenders use FICO® to determine your creditworthiness.
But even then it is difficult to say which score lenders will use because there are 16 different versions of the FICO score and four different VantageScore® versions. Credit scores are also based on data from credit reports compiled by credit bureaus. These are never identical either, so credit scores vary.
Experian® recommends monitoring different scores based on different needs: FICO Score 8 can be used to monitor your credit. FICO Bankcards 8 and 9 are widely used by credit card companies. FICO Scores 2, 4, and 5 for mortgages, and FICO Auto Scores 8 and 9 for car loans. These scores are merely indicative, as every lender’s preference varies.