The better comparison is a complete installed scope: exact product, underlayment, flashing, ventilation, tear-off, labor and warranty.
Material systems differ
Metal panels, trim and fasteners are not equivalent to shingles, starter, ridge materials and accessories. Ask for exact product names in both proposals.
Installation labor differs
Panel type, penetrations, valleys, roof geometry and edge details can change installation time and skill requirements.
Tear-off must be matched
Make sure both quotes make the same assumption about existing roofing removal, deck condition and disposal.
Model both options
Switch between asphalt and metal in the Roof Replacement Cost Calculator to see how the planning range changes before obtaining local bids.
Think beyond upfront price
Expected ownership period, maintenance, appearance, climate and insurance considerations may matter alongside initial cost.