What's the easiest way to resurrect deceased sims now?

Magic - as usual - is the easiest way (besides outright cheating). The potion might be an easier sell than the spell itself (given the progression necessities), but either way it's easier.

Death flowers, pleading, and Voodoo Dolls require you being there as they die.
The Book Of Life requires forethought.
Ambrosia requires work.
The Whispering Wishing Well requires monetary sacrifice (and even then it isn't guaranteed).