This is a great question and an excellent thread. When I first read the question I thought "Tua of course" but some of the commenters made great points in Jalen's favor. Tua will definitely prevail on yards per pass and pass completion percentage, but Jalen is likely to get much more playing time, so it could be close. I think our D will be much better, which means that some games may be even bigger blowouts than last year, and Tua may get pulled even earlier in a lot of games. I also think CNS may want to maximize the opportunity for both Taulia and Tyson to get some in-game reps, and each could play a lot in four games without losing a redshirt.
Even though Jalen will get more snaps, and face weaker defenses, to me the deciding factor is the quality of our receivers. With Jeudy, Ruggs, Smith and Waddle back and another year of chemistry between them and Tua I just think his passing efficiency numbers are going to be so ridiculous that he will lead the nation in most passing categories, possibly even in total passing yards, even if he plays less than last year.