Final answer:
Priority Mail Express is the USPS service that offers next-day or second-day delivery any day of the year.
Step-by-step explanation:
The USPS service that provides either next-day or second-day delivery 365 days a year is c) Priority Mail Express. This service is known for its fast delivery times and includes a money-back guarantee if the package does not arrive on time. Unlike other USPS services, Priority Mail Express is available every day of the year, including weekends and holidays, which makes it the quickest delivery option provided by USPS.