Personally I like Black Phantoms. I have heard that Black Skirts can lose there color as they get older.
But the one thing I have never read of any other tetra doing that the Black Phantom does, is change colors. They can go completely utterly black in a matter of seconds and then back again.
Your question was "best tetra" - I had assumed you meant what was my opinion of the best, if you are looking for a rugged, easy to keep, and damn fine looking fish, the Black Neon is hard to beat - a very under-rated fish.