I thought Ballard might have been a bit higher, but DTs 3 through 7 are all excellent and all had substantial NFL careers.
Ott vs. A. Nelson is an interesting debate (5 vs. 6 on the list). Ott's high was probably higher (early 2015, pre-injuries). But A. Nelson was a force for 2 straight years, and showed flashes as a RS Fr. I would probably give the nod to him.
How about Parker Hesse? That is a tough list to crack, and not sure who he would displace, but I get a sense that the Iowa coaches might have him higher on the list than the media do. He might not flash in the sack/TFL #s like some others, but I think he impacted the defense in many subtle ways (absorbing blocks, spilling action to the LBs) and not-so-subtle ways (interceptions, sniffing out draws and screens, etc.).