If Tate had quit after Empire and they'd called it a day, Queensryche would hands down be my favourite band of all time.
If the albums Q2k, Mindcrime II and American Soldier didn't exist and DeGarmo and Tate had quit at the same time, meaning we got Promised Land, HiTNF and Tribe, and then they'd called it a day, Queensryche would probably still be my favourite band of all time (as it is Rush are, whilst Devin Townsend is my favourite artist).
The two most recent efforts are much better than the Tateryche albums (which I tend towards including Q2k as part of) but LaTorre doesn't have DeGarmo or Tate's way with lyrics and they miss DeGarmo's gift with melody and texture so much.
As for Metallica, at one time I could play an awful, awful lot of their first 5 albums on the guitar - so much fun to play along to - and yet I'm not sure how much I ever actually just listened to their first 3 records. After those 5 it's been a mixed bag. Load/Reload were ok, St. Anger was laughably bad in every way and Death Magnetic sounded like a band doing a good imitation of early Metallica who'd employed a half-deaf producer.
The drag factor of Dedicated To Chaos ought to tip my vote towards Metallica, but... St. Anger.
So, my vote goes to Queensryche.