If you want the max strength the actual military type (not mil-spec that every ad claims, search for Type III Mil-C-5040) is the best. It has a strand of colored fibre inside instead of all white so you can tell the difference. I bought some and its much stiffer and stronger than the regular, but less easy to tie and wrap stuff with. So I guess it depends on your use. I bought a 1000' spool of USA made OD green for $50ish and Im happy with it. I bought it from supplycaptain http://www.supplycaptain.com/index.cfm/product/756/1000-ft-spool-combinations-of-colors-550-paracord.cfm
So I read somewhere that technically you can rappel from it. I'm probably not going to try. I did ask about that in a climbing store where they sell the crazy expensive stuff and even there they didn't recommend anything less than 8.5mm static.