The best overall supp I have tried is Hemavo2 max og.
Individual Ingredients: Nitrates definitely (KNO3 or Nitratene).
I do like agmatine and citrulline ( both malate and ffa), as well as glycerol, but imo the most underrated supplement for a grainy looking pump is food grade vegetable glycerine. It is very cheap, sweet, and makes all kinds of veins, large and small, pop out of my arms, abs, and recently hams according to some guy at the gym ( Don't know how or why he was looking at my hams, but I was doing ham curls, so I guess it's possible that my shorts were a little high).
A combination of all of the previously mentioned ingredients works wonders.