The interest rate is the price of borrowing the loan principal. The APR adds in origination fees, discount points, mortgage insurance, and certain other finance charges, amortized over the loan term.
For a California borrower comparing two loan offers, the APR is the better apples-to-apples number — but only when comparing the same loan program, same term, same loan amount. A lender that quotes a lower rate but higher fees will show a higher APR.
Caveat: APR can be gamed through discount points. A lender might buy down the rate with points that most borrowers would never pay back over their actual holding period. The right comparison is rate + total closing costs over your expected hold period, which your broker should walk through with you.