No single provider gives you 90% email coverage, accurate phones, and fresh firmographics. Waterfall enrichment chains providers per field: try the cheap one first, escalate if it fails, validate before accepting.
The key discipline is measurement. Per-field, per-provider coverage and accuracy dashboards. Without them, you are guessing which provider earns its place in the waterfall.
Start with a pilot: 50 rows, measure coverage and cost, then scale. Kill providers that do not meet the accuracy floor. Promote providers that punch above their cost.