Prior to the advent of the Browning BLR, the M99 was the strongest and most accurate of all lever action rifles, overall! The .250 is the best of the two chamberings you mentioned for accuracy, but the .300 is plenty accurate enough. However, the .243 Win. or .308 caliber 99's use ammo more easily available aroung the country than the .250 or .300, both of which are in the "semi-obsolete" class. If you get a .250, try to find one with a 1/10" twist, as the 1/14" twist will only be accurate with 87 grain bullets.