Some functions, like convex-hull computation or graph visualization, are implemented in several fashions, using different algorithms, libraries, or visualization engines. The choice between the implementations can't always be made from the sole algorithmical complexity point of view; instead, you are allowed to establish own preferences, based on your subjective taste.

Let's recall that preferences can be manipulated in two ways. Permanent settings introduced by prefer statements in the rule files or prefer user comands, are stored in the user's private file ~/.polymake/prefer.pl. Temporary changes are made by calling user functions with the same names as the top-level labels. They hold until the user script finishes, or the input line in the interactive mode is interpreted completely.

The top-level labels defined in the application topaz are:

default, geomview, javaview, postscript

default
for algorithms shipped with polymake, as opposed to those imported from external software packages
lower levels:
default.homology, default.triangulation, default.volume
javaview
Use JavaView - default tool for the visualization of 3- or 4-dimensional geometric objects.
Recently you can also use it for graph visualization. The 3-d spring embedder starts with random node placement, so you have a chance to get various embeddings when trying it several times.
lower levels:
javaview.geometry, javaview.graph
postscript
Create a PostScript (tm) drawing and show it with your favorite viewer (default is gv.)
lower levels:
postscript.gale, postscript.geometry, postscript.graph, postscript.lattice
geomview
use geomview - an alternative tool for the visualization of 3- or 4-dimensional geometrical objects
lower levels:
geomview.geometry, geomview.graph