Norm depends on price range. There are exceptions, but basically the cheaper the bike, the more likely you are to encounter traditional cup & cone bearings. Higher price tends to bring more cartridge bearings with it.

Efficient is tricky. Cup & cone are more forgiving for production spread. Takes longer to assemble but you can use crappier stuff.
Cartridge bearings are faster to install, but you have to run production at tight tolerances.
A factory with good machines and high salaries would want to use cartridge bearings. Low salaries and poor machines, go for C & C.
Brand new cartridge bearings can have comparably high seal drag compared to cup & cone designs.
The big thing is that bearing drag is such a tiny proportion of overall drag to make the question entirely academic apart from the most extreme and clear-cut racing applications.

Serviceability is also a so-so thing. Sure, C & C can be disassembled, cleaned and relubed. That's fine as long as you aren't getting pitting and grooving. Those things can be definite showstoppers.
Cartridge, then it's a replacement job. Different designs reach different levels of user friendliness, but as long as I have the spares available, I reckon swapping bearings in my one cartridge bearing wheelset is about a 10-minute process.
But of course I'd find some reason to touch up spoke tension, clean & relube the pawls and whatnot while I'm still in there, which'd extend the process....