Can't beat Marshalling Yard 1 & 2, all of the RPD music, lab music and most of the ambient cut scene music from RE2. Completely unique and captivating. There is no other music that sounds like that. The harmonic complexity and weird tonal intervals are a stroke of genius. To me, RE2 music is a big part of why I fell in love with the RE series.
RE3 has tons of amazing atmospheric tracks as well.
Not as big of a fan of the CVX music as most here.
OG RE has classic themes and lots of ambient space. REmake captures and expands on it well aside from the fact that it's missing some of the main mansion themes, or they come in a minute too late in the track and seldom get to hear them.
RE5 and RE0 are the underdogs