I've had some issues with FedEx overnight. One thing that irks me is, after paying multiple times for "Priority" service by 10:30 a.m., it shows up at 12:00. Asked the driver about this, says he makes only one run to my neighborhood. Basically he said not to pay extra for Priority as it won't make any difference.
Another time they dropped the ball on two overnight packages. They were going to deliver them next day (i.e. like a two day air instead of overnight). My wife and I raised some hell and ultimately they did get it to us that day, arriving around midnight by courier. Appreciate their effort, but lost a bunch of awesome corals and two fish. DFS was great as usual and got a credit but still felt terrible about the loss.
I've had really good experience with UPS and DHL overnight service, both arrive much earlier (by 10 a.m. without paying extra) and no delayed deliveries.
I'll stop short of recommending DFS abandon FedEx for overnight deliveries, but some having customer select DHL or UPS overnight as an option would be wonderful even if it costs a bit more. At least where I live, they both have far superior overnight service compared to FedEx.