What is ORTEP?

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.