There are one or two tangs that a 70g suits well. A 75g would suit a few more types though.
The ones you can house in a 70 are:
1. Kole Yellow Eye - most commonly housed in a tank of this size.
2. Bristletooth Tomni - Second most common I've seen.
Liveaquaria lists two more, however if you are to do one, I'd recommend one of these two.
Also, I've seen a few tanks of this size house a mandarin successfully. They are well established and have been raising pods
in them for years though. There can't be any other fish who will compete for pods