What is the best software of crystallography?
The question is too vague to be answerable. Doing what,
precisely, in crystallography? If you just need to determine the
Bravais lattice constants, you might contact Iowa State and try to
get a copy of BLIND and/or ALICE. For protein crystallography,
X-PLOR is pretty much the "gold standard" (disclaimer: I used to
work for the company that sells it, but that doesn't make the
statement any less true). For generating images, there are any
number of packages out there with plusses and minuses for each, but
I'm rather partial to ORTEP even though generating the input deck
for the desired view is kind of a pain in the rear involving a lot
of trial and error. PLUTO is easier to use, but the images it
generates aren't (or, at least, weren't at the time I was using it)
as nice as ORTEP.