Might as well learn to load on the existing brass. Depending on the chamber dimensions of your rifle, you may get limited life from any brass without annealing. Factory chambers are often on the large side leading to lots of "movement" from sized to fired.

As already mentioned, sort by head stamp and load the biggest quantity. Load the rest for practice ammo if you like.

Brass is a small contributor to accuracy when compared to shooter skill, barrel quality, trigger quality, consistency of powder charge weight, and bullet selection. I wouldn't worry about it until you've worked through those other factors first.