The best you can get as far as strength right now is RWS. Not it weighs 48 gr more per case than RP so your case volume is down a bit. RWS is strong and you will see good velocity at a lower charge than some other brass. Usually I need to run 4 grains less powder to keep the pressure down but velocity is the same.
They do not make Lapua brass for a 300 win any longer, but I have found some on accation. It is simply the best and is awesome to load with.
Third, WW will also do the trick and is less expensive but simply will not last as long.