Rogue 66 or Quicksilver

which of these preamps would give me the better sound?
No one can answer that question for you. It depends upon your taste, your room, and your other equipment. I think they are both good pieces of equipment, each having its own sound. I personally prefer the Quicksilver (which I think has a warmer, more tube like sound). I don't think you would really go wrong with either of them. And there are other choices out there for about the same money. But if I was limited to those 2, and it was my money, I would choose the Quicksilver.