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 polytope are:

beneath_beyond, cdd, default, geomview, javaview, lrs, porta, postscript, qhull, splitstree, topcom, vinci

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
cdd
Use the double description method as implemented in cddlib. It is the default algorithm for computation of facets from points or dually. It operates with arbitrary precision arithmetic (GMP).
lower levels:
cdd.convex_hull.dual, cdd.convex_hull.primal, cdd.convex_hull.redund, cdd.simplex
lrs
Use the reverse search method, as implemented in lrslib.
lower levels:
lrs.convex_hull.count, lrs.convex_hull.dual, lrs.convex_hull.primal, lrs.convex_hull.redund, lrs.simplex, lrs.valid_point
beneath_beyond
Use the sequential (beneath-beyond) convex hull algorithm. It performs well at lower dimensions and produces a triangulation of the polytope as a byproduct. There is no dual (vertex enumeration) implementation of this algorithm.
lower levels:
beneath_beyond.convex_hull.primal
porta
Run the porta program, implementing the Fourier-Motzkin elimination method. The essential drawback of this tool is that it employs a limited-precision arithmetic, and therefore can fail on numerically difficult problems.
lower levels:
porta.convex_hull.dual, porta.convex_hull.primal
vinci
Use the vinci program for volume computation.
lower levels:
vinci.volume
qhull
Use the UNKNOWN LINK: external.qhull program for convex hull computation.
lower levels:
qhull.convex_hull.primal
topcom
Use the TOPCOM package for computing polytope triangulation.
lower levels:
topcom.triangulation
splitstree
use the SplitsTree package