A shortlist per category, ordered by rating weighted by how many merchants left one, drawn from the full App Store catalogue rather than from a handful we happen to know.
SEO apps cannot create the content or earn the links that decide rankings. What the good ones do is remove technical obstacles at a scale you would not want to handle by hand.
The most durable channel a store has, because you own the list. The pricing model you pick at 500 subscribers decides what you pay at 50,000.
Loyalty rewards frequency. If most of your customers buy once, points expire unused and the programme becomes a discount on first orders.
The app works as advertised; the strategy behind it is what destroys margin. A discount taken by someone who would have bought anyway is pure cost.
One technical decision made at install time - whether reviews render into your page or inside an iframe - determines whether they can ever show as stars in search results.
Post-purchase offers cannot damage an order that already completed, which is why they are the safer place to start. Judge them on revenue per visitor, never on attach rate.
Bundles reliably raise average order value and just as reliably break inventory accuracy, depending entirely on whether they resolve to real line items.
Installing more analytics usually makes you less certain, not more. An app earns its place when it answers a question Shopify's own reporting cannot.
A confident wrong answer delivered instantly costs more than the ticket it saved. Measure these on resolution without follow-up, not on deflection.
Want the reasoning rather than the shortlist? The buying guides cover what to compare, what changes depending on what you sell, and the mistakes that cost most.