The first thing to consider in ball selection is that the patterns at Nationals are generally not heavy oil. They're flatter than most THS conditions, so they give the illusion of being heavier. The area around the 5-10 boards where most THS bowlers live is OOB at Nationals. You have to target the friction 40+ feet down lane and play tighter with a controlled reaction if you want to find any success.
There are no absolute rules for ball selection, but upper mid-range symmetric solids with 2000-3000 grit surfaces match up well. I had some success with a Columbia Disorder in the Open, as well as the side tournaments (BJ and BTM). Some of the other balls mentioned here (Covert Revolt, Forza, GB2, IQ Nano) fall into the same category.
A lot of bowlers fall into the trap of throwing their favorite Asymmetric hook monster at 1000 grit. Before you know it, they blow open the mid-lane, messing up the shot for themselves and everyone else on the pair.
Trust your ability to repeat shots without trying to create a lot of area. Select a ball that helps you achieve this objective.