what rear would you go with

well the 3:91 is going in my sons Dart 340/4 speed when he gets it done. I just swapped it into mine to get away from the 4:10. I didnt see a whole lot of difference. That is why I was thinking about going to a 3:55 but I am now leaning on putting the 3:23 in replacing the 4:10 and selling the 4:10 gears. They don't even have 500 miles on them. I still have the box and packing stuff from them. But I am a little older now since I had 4:10's in my 64 Chevelle.