RID is the most undetectable by far (MTA, Blacksmith, Pest Control).
If you want the most undetectable bot for a variety of skills, I would go with iBot Pro (RSCheata.net, $15/month) or SCAR (Villavu.com, Free).
And RSBots.net/RSBotting.com do not even since their scripts are so limited, so don't even think about saying that they are the most undetectable.