I can’t prove scientifically that I am right, but it seems to me
that easy solder eats into silver in a way that harder solders don’t.
What that means is that in areas where solder has flowed that I don’t
want it, it may actually end up flowing back out and leaving a low,
I use the three-solder method, with most seams in medium. Making a
bezel (soldering the ends of the bezel strip together) should always
be done in hard because, since the bezel is so thin and sticks up
from the heavier back plate, it is pretty easy to melt the solder out
of the seam. This can be fixed, but what a PITA!
Bezel to back plate, and nearly all other seams, I use medium. Last
fiddly things after the bulk of the work has been done, I use easy
because I really don’t want to waste all that work!
That’s my method-- YMMV!