If you have to do it, do it to the mix. If you do it to each individual track, you will end up having to turn all the faders way down to avoid clipping the mix buss.
Food for thought: When you mix two signals at -6dbfs together, they add up to 0dbfs. Three tracks at -6dbfs = +6 (severly clipped) If you normalize all your tracks, you are going to have to back them all way down (with the faders) to keep from them adding together and clipping the mix. So you are just wasting your time trying to get them loud just so you can turn them down in the mix.
All normalizing does is turn the whole track up until its peak is a 0db. It just changes the volume, there is no quality benefit and it doesn't change the sound.