I also started with the CTX series and the Body Blast Timesaver DVD. However, I as well was already working out regularly and at a more advanced level. The CTX series was great for me since, as mentioned, the cardio segments are all around, if not less, than 30 minutes long and you only work out one body part per workout. I have not tried the Basic Step and Body Fusion, but I agree that I think they are for "beginners".
Katie