Fed Ex is more expensive in my previous shipments.
Which has a higher loss of packages? Can't answer that one, and I doubt you'll get anyone with any real info on this.
I've received literally 100s of EMS packages and only ever had 1 damaged. Seems like a good service to me personally.
Fed Ex, because of the expense, doesn't see much use from me. I've received a bunch of packages and never had one damaged, so take that for what it's worth.
EMS ships 365 days a year (at least in the US). Sunday and Holiday delivery is free, it all just depends on when the package gets to the local distribution point. Fed Ex charges for this service.
UPS, even though you didn't state it as an option, has almost always delivered a package that looks like shit. Rarely are the contents damaged, but I can definitely see how they could easily be damaged.
EMS is handled by the Post Office in the US, but it is handled by the post office or a 3rd party in other countries. I believe the UK uses a 3rd party, not their postal system.
EMS is usually pretty damn fast as well, with packages from Japan reaching me in MD in 3-5 days, usually 4 days.