Polyurethane and nylon solve different operating problems. The right choice depends on the floor, load and environment rather than color alone.
Polyurethane wheels
Polyurethane wheels provide quieter operation, good floor protection and useful grip.
Nylon wheels
Nylon offers low rolling resistance and high load capacity on smooth floors, but it is harder and usually produces more noise.
What to send for confirmation
Provide the pallet jack model, wheel position, dimensions, load and floor condition.