Grados are sure fantastic for jazz and rock, and good for electronic.
I don't quite know about rap, but it is not bad. Grado is a very good sound value for this price, especially 60 as I read on the forum. I tried a 497 and I've been deeply disappointed !
But the problem is that grado are really opened back. For what kind of travel ? Train, bus, plane ? 'cause I own a MS1 and I admit that they really leak the outside sound, in the subway especially. And in a plane, it would be a bit disturbing for your neighbour. It is not dramatical if you don't force the volume.
If you don't care about that, then go on with Grado.