If he doesn't have Throw Spiral (i.e. Throws Tight Sprial: No, and make sure you check, don't just go by it showing up on the list of things you can buy), I'd get that. It seems to impact drop rate by receivers and overall accuracy.
Otherwise, I'd focus on the accuracy ratings that match your passing game, but I'd want SAC at least decent and MAC solid as well.
Depending on how the kid starts tells you where to go. For example, Danny Martens is decent at SAC, bad at MAC and excellent in DAC. I throw a lot of intermediate-depth passes (deep ins, deep outs, comebacks, skinny posts) so I needed to focus on that MAC. Having decent SAC always helps - accurate dumps offs, hit the slants in tight windows, hit curl-flat route combos consistently - good way to move the ball even if your run game is struggling. Someone like Andrew Luck just needs AWR, basically. Someone like Terrelle Pryor needs some of everything. On one hand, he's a project in every sense of the word. On the other, he's a blank slate, ready to be molded into your scheme if you can be patient enough with him.
After that, it still depends on your offense. I like to have a run game, so adding PAC helps. If you like to roll out or escape to buy time, TOR always helps to be decent. Don't need to get it up to RG3 level, but enough to where you can hit some guys that come free as you scramble around 10-12 yards out or someone leaking out.
THP is another "depends on your offense" rating. A vertical game with speed merchant WR is going to need THP. THP also helps on tough throws like deep outs and corner routes. If you're aggressive, i.e. you like to fit the ball into spaces, THP is your best friend - lowers reaction time window for the defender.
If you're a more West Coast/short-medium pass style QB that plays it more safe, THP only needs to be decent. I used Coly McCoy well with a West Coast style offense. He was not good at doing a deep out, even if it was accurate. Defenders had too much time to recover, even if beat on the WR's route itself.
AWR and other traits DO help even if you play the games out, but I would focus on them only after the above are solid. Force Passes might be the most important as it seems to impact INT rates. This is what I think AWR impacts as well. Seems defenders make fewer "great plays" against QBs with higher AWR.