Assuming your going to use one of them more than the others the classic upside-down t, would probably be the best idea.
If you will be using them all equally, you may be better off with the 2-by-2 square, this way they are all equally difficult to look at. Or if you are going to use 2 most of the time you could adjust it so that two of them are at eye-level, with the other two sitting just above them.
Another option is the simple straight line, which would be good if you will be working on one screen for a while, then switch to another one, etc.
I would probably just use 3, one main one, and two on either side. With maybe one more above the others that just has some statistics, that are updated periodically. It could even be from another computer.