Is first-class USPS delivery slower? Yes it is. We tested it.
The Los Angeles Times tested first-class U.S. Postal Service delivery. The results? Spotty at best, dismal at worst. First-class mail delivery has slowed markedly. The Times found that one-day delivery within Los Angeles County is all but gone. Service between Southern California and the San Francisco Bay Area is inexplicably bad; a third of the letters mailed from various Los Angeles County post offices to Millbrae took a week to arrive. Many letters sent to Washington, D.C., and Austin, Texas, took six or more days to land.