Proper type of tubing for trans cooler lines?

Nycopp (nickel copper) is what I would use if I was hand bending my lines.

There's absolutely no downside to them, only pluses. No corrosion, easy to bend and flare, high burst pressure.

Trans cooler lines are low pressure, 30psi, but I wouldn't trust copper line on something critical. Steel rusts, and SS is hard to bend/flare.