Unless this is a numbers build I personally like the ones that have a hex on them for tightening/loosening. I went with 5/8 on both of mine as then I would not have to neck down/up to get into the heater core.
I am trying to make it a numbers build as close as I can. I will go with the hex if I have no other choice. Once it is painted blue I am sure it will look good and most would not notice. I would just know that it is not correct.
