For hip-hop and r&b, you'll want to experiment with every type of scale. If you want that classic rap sound, you'll have to draw from jazz, soul, funk, blues melodies. Blues is interesting in particular because so much music evolved from it. Personally, I've made beats using the blues scale, minor and major. Unfortunately, I could not tell you other scales I used because I cannot remember without opening many of my beats. Hip-hop is so broad and everyone has their own adaptation of what they consider a hip-hop beat. It really depends on what you are trying to achieve because the scale has a direct influence on the feeling and style of a beat. Just don't limit yourself and have an open ear for the music of yesteryear. One good idea I just thought of..is take your favourite songs and analyse those. I know this is basic but maybe you'll learn a lot by analysing just one riff or loop or whatever that triggers your interest. Good luck