FWIW Quiet Arts Wave Rider 2 plug in is what I use to keep levels consistent. In ProTools it runs as a midi controller, literally moving the fader up and down in response to audio levels on whatever track you set. The beauty of this is zero compression – the dynamic range remains intact.
I find Waves Vocal rider does add a touch of compression.
ERA Vocal Leveler is basically a compressor, like an AGC.. I tried it today, but have no use for it.