Two or three for most businesses. ChatGPT and Google AI Overviews cover the majority of volume; Perplexity matters in research-heavy B2B categories. Tracking all five when two are relevant is a measurable waste of budget.
Engine relevance is category-dependent — check where your buyers actually are before paying for coverage.
Each engine cites differently, so results are not interchangeable between them.
Adding an engine later is straightforward; the prompt set does not change.