Both F45 and Orangetheory are excellent choices for HIIT workouts. F45 focuses more on functional strength training circuits while Orangetheory specializes in treadmill-based cardio training guided by your heart rate zones. F45 is great if you want to improve overall fitness across modalities. Orangetheory gives you more optimized cardio and endurance training. Try out both studios if possible, since preferences vary by individual.