Is a high-yield savings account or a money market fund better for my emergency fund?

Both are reasonable, and the differences are subtle. A high-yield savings account is a bank product covered by FDIC insurance up to the standard 250,000 dollar limit; it is simple, and your balance never fluctuates. A money market fund is a mutual fund held at a brokerage; it is not FDIC-insured but instead has SIPC coverage and invests in very short, high-quality debt, and government money market funds are considered extremely safe. Money market funds sometimes yield slightly more and settle inside a brokerage where you may already invest, while savings accounts offer instant bank-to-bank transfers and government insurance. Many people use a savings account for the instant-access tier and a money market fund for the larger, rarely-touched portion. Pick based on where you want the money to live and how fast you need it.