To prefer the non‑high‑delay ISP link (when both ISP links are up) in BGP with default attributes, which attribute should be changed?

LOCALPREF is the correct attribute because it is a well-known discretionary BGP attribute that influences outbound traffic from an Autonomous System (AS) to other ASes. A higher LOCALPREF value is preferred. By setting a higher LOCALPREF on the non-high-delay ISP link, the router will prefer that path for traffic leaving the AS. AS-PATH is a well-known mandatory attribute that influences inbound traffic and is used to prevent routing loops. WEIGHT is a Cisco-proprietary attribute that is local to the router and influences outbound traffic, but LOCALPREF is preferred for influencing traffic throughout the AS. MED (Multi-Exit Discriminator) is an optional non-transitive attribute used to influence inbound traffic from a neighboring AS.