Have you done either before?
I've never done 30 Day Shred but I have done Tae Bo and I will tell you that it is very intense if you aren't used to it. It is a GREAT workout and when I popped it in a few weeks ago (after not doing it for a couple years), I had to stop it 12 minutes in because I was getting sick (and I was going slower). If you HAVE done it before, I definitely suggest to go ahead and do it. If you haven't, just do what you can :)