It depends if you are a beginner or if you are more advanced.
If you are more center on stepping and not going to do any weight training and a beginner I suggest you get a smaller step, which is called a circuit step.
But, if you are going to do weight training too I suggest you get the bigger step. You will be doing exercises that you need a bench and the gym Step is perfect for this.
There is a step from SouthernGirl. But, it is shorter in length and the top has a weird material on it. That material is soft and I found I could slip on it. And when you do it with risers it moves.
I like TheStep with the bubble cover. It is rubber and not plastic like the old step on it. And that step doesn't move as much.
If you have the big gym step you could modify the movement. Instead of going to the corners, go to half the distance and work yourself up to it.
Hope this helps,
Jennifer Denny