Ant baits come in a few different forms, liquids, solid matrices and granules. Liquid is an ideal formulation for killing ants that are typically co-existing with honey dew producing insects. The Argentine ant for example will consume more ant bait in the liquid form versus the solid. Particle sizes are also important when considering an ant bait granule, as some ants may not be able to pick up larger grit sizes.
The type of ant killer that is recommended will typically depend on what type of ants and also their food preference. Another important factor is sanitation so that the bait is not competing with other food sources; remember that the bait is trying to mimic the ant's food source.