Why splitting the budget doesn't work
The instinct is understandable. Three platforms exist, so it feels safe to be on all three. But ad platforms need a minimum flow of conversions to learn who to show your app to, and a small budget split three ways starves all of them at once. You end up with three half-trained campaigns instead of one that works. Concentrating the budget where it has the best shot, learning, and then expanding is almost always faster than spreading thin from day one.
What each platform actually does
To choose, it helps to know what each platform actually does. Meta and Google App Campaigns are discovery engines. They show your app to people who weren't looking for it, based on behavior and signals, which is how you reach scale and audiences that don't know you exist yet. Apple Search Ads is the opposite shape: it catches people typing into the App Store search bar, so the intent is already there. The volume is smaller and it's iOS-only, but those users are often a short step from installing.
So the real question isn't "which platform is best." It's "where do people like my users decide to get an app like mine." If your category is something people actively search for ("budget tracker," "habit app"), Apple Search Ads can punch far above its size on iOS. If your app solves a problem people don't yet know to search for, discovery on Meta or Google is where you create demand. Most subscription apps end up using more than one eventually, but "eventually" is the key word.
Separate systems, separate economics
There's also a structural reason not to lump them together, the same one that trips people up with iOS and Android: these are separate systems with separate economics. We've seen install costs vary by more than 4x between platforms for the same app in the same week. Running them as one blurry "app marketing" line hides which one is actually working.
The honest sequence: start on the single platform that best matches your users and that your budget can feed to the learning threshold. Get it to stable, profitable conversions. Then add the next platform with its own budget and judge it on its own. Three platforms done in sequence beat three platforms done all at once and all underfunded.