Trans Fluid to Use?

I just bought a rebuilt 600HP trans, I was wondering what trans fluid to put in it. My buddy says Valvoline ATF +4, I only plan to use it on the street, might take to the track once or twice to see what it will do, but not interested in racing at all. It will be a good street car, but should mention I'm in Tx where the heat gets to 105+ in the Summers. I do have a deep pan and a trans cooler to help out.

Oh, and what brand?