Toner (Laser Printing)
A powder that is "fused" onto paper. Fast, fade-resistant, and cheap at volume. Ideal for documents.
Ink (Inkjet Printing)
Better at reproducing color and gradients — suited for photos and graphics. But it costs more per page and is sensitive to idle periods.
Which Is Cheaper
For high document volumes — laser. For occasional color/photo printing — an inkjet with a CISS.