Santa's sleigh delivered more on-time packages this holiday season, though a few retailers still broke their promise to get shoppers their online orders by Christmas. According to data from customer service analytics firm StellaService, 7 percent of packages did not arrive at their destination by their promised delivery date. That compares with 12 percent last year. What's more, the improvement came even as retailers and delivery services were dealing with a surge in volume compared to last year. StellaService compiled its data by ordering four items from 40 of the country's top retailers, shipping each of the four orders to different regions around the U.S. It placed the orders on each retailer's standard delivery deadline for guaranteed arrival by Christmas.

An employee sorts packages at the UPS Worldport in Louisville, KY. Jodi Gralnick | CNBC