I'm not sure if you was talkin about beats or who to sample on rb, so i'll just answer both. Beats, definately somethin with slow and strong bass for a slow track, and for a fast or medium paced track, i'd use somethin new with fast snares and drums with a use of pracussion instuments. But for samples in audio, which you might already know of is spliviticus, sk!llz, & i mind theory's ok.
~1~