The best 30-day workout for getting in shape?

Which 30-day fitness challenge or get-in-shape program did you find to be the most successful?

T25 + Eat Right: A high-protein diet is what I advise; avoid processed foods and limit your intake to fruits, vegetables, and proteins. Plan your meals and, if necessary, prepare them.

Body fat decreased from almost 23% to roughly 13% between 160 and 145.

Thanks, are there any other options to T25?