Free apps live or die on the balance between ad revenue and user experience — push too hard and users churn before they ever generate meaningful lifetime value.
Start with frequency, not format
Most "annoying ads" complaints are really frequency complaints, not format complaints. A well-timed interstitial every few minutes is barely noticed; the same interstitial on every single screen transition feels hostile. Before switching formats, most apps get more mileage out of simply capping how often any given format can appear.
Reserve the most intrusive formats for the least disruptive moments
Save full-screen formats for natural breaks — level completions, content transitions, app launches — rather than mid-task. Pair that with a persistent low-yield format like a banner to keep a revenue floor without adding any extra interruption at all.