The intention is in future releases for STILTS to provide all the plot types and facilities which are available from TOPCAT. STILTS may additionally offer more detailed options for controlling plot appearance, for instance of font and colour selection and tick mark placement. At time of writing however, only the 2d scatter plot, 3d Cartesian scatter plot and histogram plot types are available, though these do include the most useful plot types and the most of the options from TOPCAT for these plot types are available from STILTS too.
As well as the advantage (in some contexts) of being able to generate plots in a scriptable fashion rather than from a graphical interactive interface, STILTS allows plots to be made from datasets of unlimited size. While TOPCAT has an effective limit of a few million rows, STILTS can stream data from tables to do its plotting, so a plot can be made representing an unlimited number of rows without large memory requirements. In some cases this might lead to plotting times which are a bit slower than TOPCAT - if this becomes an issue something may be done about it.