i also use s&b, geco, sk and cbc brass all mixed, but they work fine for me, only the sk is a little bit difficult to seat the primers, but s&b uses a new type of brass since this year, in wich it is more easy to seat a primer, but i only use mixed headstamps for training, for matches i use only cbc brass.
i also find it more difficult to seat murom primers, than federal primers.