U-Pack is freight-based and fast, charging by the linear feet you use in a trailer. 1-800-PACK-RAT gives you a steel container with a flexible loading window. Speed and price versus loading comfort is the real decision.
Verdict: U-Pack for the cheapest fast cross-country move if you can load in 3 days. 1-800-PACK-RAT when you want a longer loading window or storage on either end.