Which of these services guarantees delivery timeframes to certain destinations?

The service that guarantees delivery timeframes to certain destinations is Priority Mail Express. This service offers guaranteed overnight delivery to most U.S. addresses, including use of a money-back guarantee for on-time delivery. It provides customers with tracking, as well as options for additional services such as insurance and signature confirmation.

Priority Mail, while it provides expected delivery timeframes and quick service, is not guaranteed, meaning that while most packages arrive on time, there is no refund if they do not. Standard Post is primarily for less urgent packages and typically does not include specific time guarantees. Parcel Select is a ground service primarily used by businesses and also does not come with a guarantee on delivery times.

Overall, Priority Mail Express stands out for its commitment to guaranteed delivery times, making it the correct choice among these options.