I really can't rank them, as they all kind of balance themselves in the end. For example, the only tracks that I can remember from RE3 is the music from the animated intro befoe the menu, when Jill is narrating at the beginning, and Never Give Up The Escape. Never Give Up The Escape, however, is one of the most haunting pieces of videogame music that I have ever heard. For CV, the only track that I can remember is the the Doll, but it's stupendous as well. I've only heard the soundtrack for the Dual Shock version of the first game, but the tracks for the Guardhouse (upstairs and basement) are amazing. RE2 soundtrack is flawless. RE4 has the mighty Infiltration, Regenerador them, and Ada's Mercenaries theme. RE5 has the great ambient African music.
Long story short, I think it's just impossible for me to put them in a list.