2.4 GHz
2.4 GHz generally travels farther and penetrates obstacles better, but it has fewer non-overlapping channels and often faces more interference from nearby networks and other devices.
5 GHz
5 GHz usually offers more channel capacity and can deliver higher throughput at shorter range, but signal strength tends to fall more quickly through walls and distance.
Which should you choose?
Use the band that gives the best real connection where the device is actually used. Close to the router, 5 GHz is often preferable. Farther away or through several obstacles, 2.4 GHz may be more reliable.
Do not judge only by the label
Modern routers may steer devices automatically between bands. The best band depends on the client device, radio environment, distance and network design.