Best tactic for boss is to stick your rdps and healer up on the platforms on the side going up to the final conversation...stick em right up there on the rails and melt the big guy as he targets. It makes the fight incredibly easy and you can really kill any of them you want that way because the 2 adds end up running up to get their target. Using the rail tactic you can kill the commander and then finish off the big guy and medium guy or you can burn the big guy before he even gets close to anyone. If you are doing this with melee dps though no question kill the big guy first.
Don't do this, it creates a completely messy situation for the tank to deal with by having adds running up the ramps etc.