If you want to strip leech patterns for Salmon, which tracks better (and is easier to get it down)and looks more natural - a tube fly tied on copper tubes or one tied on a plastic tube with a weighted cone head?
Not really the right question, as in everyday fishing they are not really interchangeable. The real question is "If you really want to get down, in fast current, and stay down, which will do the job better" A copper tube of any length is going to ride ass down. It will not "swim" as well as a conehead. You will likely loose it a lot sooner on the bottom. But it can be a trip saver if you're going on a trip of a lifetime to BC, Alaska, Europe, or Scandahoovia. 12 years ago, when I got heavily into tubes also coincides with when I moved here. I sent a former co-worker in the shop I left a dozen 2.5 inch purple tubes tied on heavy copper. 2 or so years later he sent me an email to say he finally found a use for them. You can guess the rest. The dean. Blown out. The flies only lasted 45 or so minutes each. But he caught a fish. Only one other guy in camp caught one.
Think about fly design if you're going to use a longish copper tube. It's going to be ass down so a single long flowing wing tied in at the head isn't the best choice. And I wouldn't spend a lot of time on them either. They hang bottom, and be sure to check the leader often for kinking and wear.
I can't really answer for that. length of cast, type of line, length of leader, all of that is going to play into it. I wouldn't want to cast copper tubes as much as I would have to with an active retrieve. For swinging on a spey rod, it's not so bad. Cast and strip a couple hundred times? Sounds awful to me, but maybe that's just me. I'd get the shortest, fastest sinking line, a short leader, and a decent cone on the fly, and start thinking about casting upstream instead of directly across.