Five models cover nearly everything: firmographic/territory, round robin, product-based, vertical, and full randomisation — most companies run a hybrid. Name your model before you pick a tool, because the blend decides the tooling. More complexity in the blend means more router.
Routing is two layers, not one. A lead first hits a classifier — what kind of lead is this? — which hands it to the right engine, and only then does the engine's own matching logic pick the rep. Keep every routing decision in one place; the common failure is logic scattered across workflows nobody can read end to end.
Every claim above comes from work LeanScale published. These are the sources.