Start with the diagnosis
You cannot compare repair with replacement intelligently until the actual fault is known. A minor component failure and a major system issue are different decisions.
Consider the whole system
Look at recurring failures, comfort, airflow, equipment condition, compatibility of system components, and whether the proposed repair addresses the underlying problem.
Compare future paths
Ask what the repair is expected to solve, what replacement would include, and what supporting changes may be necessary. The best option is the one that fits the diagnosed condition and homeowner priorities.
Safety note: If you smell gas, see smoke or fire, suspect carbon monoxide, or believe there is an immediate safety danger, leave the area as appropriate and contact the relevant emergency or utility service. Do not treat an active safety emergency as a routine HVAC appointment.