Robbins is making a good top. I bought one several years ago that has a poor fitting back window, but I understand they have corrected the problem. It is probably the closest to original that you will find.
Much of the decision is your preference and how much you want to spend. I've installed a TR3 top, but not the 6. The 6 is more involved since it is integrated with the frame. The job is time consuming more than hard. If you make a mistake, you live with it.