Which one of FB's longer workouts do you think is best as a monthly endurance challenge?

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Personally I've been enjoying the 1000 calorie workouts as a once per month treat but I'm starting to look for something different. Gonna try one of the 1 hour HIIT workouts this time around to add more variety. What are your thoughts on them? and which hard endurance workouts do you enjoy doing the most as a once-in-a-while challenge?