Hi Angel!
This would depend on which workouts you do. If you plan to do the step workouts, Imaxes, Body Max, etc., you would want the club step. But...
I had a couple of 8" aerobic steps along with many of the Firm high steps (the square one, the incline one, the Transfirmer), but I wanted a longer step and one with better shock absorbtion for my knees so in early June I purchased the original Club step and I LOVE it!! Since then, and since the risers are compatible in the club and high step, I purchased the high step as well. This way, I can mix and match the risers to get different step levels. I have since gotten rid of the other steps. It's nice to stack all the risers up and the two steps now take up much less room.
Which workouts do you have?