Traditional P if just one pickup, reverse P if there's a bridge pickup too. The traditional orientation gives you more range (goes lower on bass strings, higher on treble strings; which was what Leo allegedly intended), so it makes more sense imo on a one-pickup bass. But if you have a bass with a bridge pickup too, I find that it works better if the P is reversed - it both blends better, and the whole range issue is moot with the bridge pickup. I think dual reverse P is the way to go in that case 
Yes, Leo for sure tried a reverse P, at least by mid-70s. He used that on one of the Stingray prototypes.
Yes, Leo for sure tried a reverse P, at least by mid-70s. He used that on one of the Stingray prototypes.
