sm7b and re20 are a good comparison
421 not so good with them two
i love 421/57 on guitars
also sm7/57 sm7 is fuller and smoother than the sm57 but not as mid hyped as the 421
i do like the re20 on vocals though, it takes less gain than the sm7b and more proximity.Overall i like the sm7b more imo.. but there very close