From an engineering stand point, there is no question inmy mind, it has to be Dallas.
Likeness is there as well, and value. It simply is a fantastic figure.
Figures like Indy and BR Joker don't even come close to Dallas IMHO. They're very cool, and have great likeness, but are nowhere near as innovative as Dallas.
Gandalf is a close second to me, because of the amount of research and the excellent materials used.