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.   

Steven,

This was very true up until they went to the new Ice oil a few years ago.  The shot starts playing up around 6-7-8 boards and then migrate from there.  One of the teams that won an eagle never got inside third arrow.  Mid performance even rolling balls have been the way to go at least in team event.  When John Gaines' team took the record team score a couple years ago; every guy on that team used Arson Low Flares playing 6-7-8 to start and finished the last game around 12-13 at the arrows.  Singles and Doubles is closer to what you mention because the pattern volume is not as heavy as the team pattern. 

Lots of good advice on this thread.  It is more about how you play the shot than what you throw, with exceptions noted.  Stay away from super aggressive surfaces, and asymmetrical balls.  My best look last year was with a cobalt vibe in team, and original IQ Tour in dbles and singles.  Trend is to longer patterns which keeps the transitions smoother off the end of the oil. 

Covert Revolt and Venom shock will be in my bag for sure.

Also I would look at the Break Down as it has the S70 cover which has always done well at Nationals.  With a surface change it should be able to work great.

Well I plan on bringing my Dream with me along with my Freakin Fanatic. Oh and my plastic ball.