It is so personal so it hard to advise anybody. Some people like P&B shakes but if you are according to Chinese and Ayurveda medicine have a "dry" body you might get constipated.
I would think the most talked about on the forums are Oxypowder /colosan, LBB from Ask Barefoot, Colonix or P&B shakes, I should add Dr.Schulze.
You could check the FAQ for more information and here is a different view from Andreas Moritz , read the whole thread
It all has to do how your body reacts, I tried Colonix and after 3 days I could not stand all that stuff in my bowels and did not feel too great, but that does not mean that for other people it might work.
Sorry that I can't give a definite answer, I figured out what worked for me.