Its not an easy answer. I do a little of both. I tend to add a little comp while mixing just to mix against a compressor then bounce it full (ie: no dither/sample rate conversion) and redo the whole deal. The trick for me is to keep it very light in the compressor during mixing because compressors are multiplicative as opposed to additave meaning a 3:1 during mixing and a 3:1 during mastering will give you 9:1, not 6:1 so you need to be careful. You could do the gain staging during mixdown if it makes you happy I really don't see why it would matter but for me its not something I focus on during mixing. As far as the difference between Logic and Waveburner its a pick you poison situation. I prefer Logic because I am more familiar with it. P.S. the Mastering video is awesome!