Mat
Pros: Portable; less expensive; harder to “cheat” because without the help of cords or springs, you must engage your core muscles even more; dont necessarily need an instructor; use your own bodys range of motion; no downtime for switching out equipment, which means your heart rate stays up and your calorie burn intensifies.
Cons: As you improve, it may become harder to challenge your body (try incorporating 1-2 lb hand weights into your mat routine to add resistance).
Reformer
Pros: One-on-one experience with a professional; good for first-timers who need special attention; improves body alignment better than work on the mat; can elevate your mat workout to a new level (and increase muscle mass) by adding resistance with pulleys and springs; also adds more range of motion to help you get more results from each exercise.
Cons: Increased downtime while switching equipment; expensive – an hour with a Reformer can cost anywhere from $55 to $100, depending on where you live and if your teacher is certified. (Visit pilatesmethodalliance.org to locate a certified instructor.)