The benefits of each are different.
FedEx Ground is faster coming from the west coast in most markets. However, if you ship a package to a residential location, they will move it to the HD service and will add costs.
USPS uses FedEx planes to (and I think UPS in some cases) to move the Priority Mail.
USPS however, while overall cheaper initially probably costs more when you add the insurance, tracking,etc. that comes with shipping UPS/FedEx.
The FedEx tracking is great if you have access to a station. There are more codes on their system then available to the general public. Not familiar with UPS's system, but it seems to work the same way.

Never ever ship a package Air if it is in the same state/local area. I had an upper level executive with an oil company mention to me at a holiday party that they use Express to ship envelopes from Northern VA to D.C. They were shocked when they were told it was not put on a plane, rather a trailer and they were still charged the higher rate.
And just because the driver gets to your area earlier does not mean they hit your customers areas early. It all depends on how the routes are routed. There are more UPS routes then FedEx routes. Different products get higher priority. I had one driver tell me they had to drive passed my location daily until the window for the service (10A.M. I think) the package was allowed to be delivered. Otherwise he would get in trouble with management for giving away product. In this case ealier delivery time then paid for.