What size or set should a beginner buy?

Reviewers repeatedly advise beginners to choose a set with a clear progression of resistance levels rather than the single cheapest band. A widely echoed warning on r/ResistanceBand is that the cheapest bands offer only a few centimeters of usable stretch before they stop budging. A 5-level loop set or a tube-and-handle set with light-to-heavy bands gives the most room to grow.