Which is best??
I dont think what determines which bar is best has anythng to do with conductivity. Its application.
If say you have a six cell touring car that requires sadlle packs-the obvious choice for your jumper is braided wire. Its flat like a battery bar so it stores in your battery box well and it has a lot of surface area and is SUPER easy to solder on-unlike a piece of insulated 14g wire. SO you run solid bars on all cells-except your jumper.
Downside of course is if you dont take care handling your bateries out of the car-the stranded wire starts to fray-but hey-put another piece on!!
Outside of that-I dont think it really matters much.