Too many variables all have to come into line to really nail it down to just one or two, or ten.
My limited experience with accuracy has been, like Ridge mentioned, find a bullet that your barrel likes, then find a velocity that runs consistently in it.
Since you're talking about factory loads, the reality is that there is no "science" that will tell you which will be the most accurate load in your rifle - you just have to go shoot a bunch of loads and figure out which your rifle likes best. If you were reloading, you could find a bullet that your rifle likes, then determine the "optimal charge weight" or "accuracy envelope" to give you the most consistency in velocity, but since you're talking factory loads, you just have to try different loads.
There are a few things you can look at, like your twist rate and barrel length (resulting velocity) to determine a proper bullet weight then try different loads in that weight range, but then you're still left trying different brands and different loads. I have two AR's with the same brand barrel that I know to be chambered with the same reamer, but one REALLY likes Winchester 50grn Ballistic Silvertips, the other is just so-so accuracy wise with the BST's but is best with Hornady 50grn V-max's. On the other hand, I have a Savage 223 that likes pretty much anything you feed it, and will post 5 shot groups in the 1's and 2's with 34cent per shot Remington 50grn UMC JHP's. Any of them are "accurate enough," but each of them have their own favorite "flavor" for the most accurate factory load.