I really like the Purple Tang. Like others have said the Powder Blue is ich prone.
I have a Coral Beauty, Purple Tang and a Naso Tang in my 125. They were in my 75 until I upsized. They all are fine with each other, the Naso and Purple are best buddies. They follow each other everywhere and they will both eat from my hand at the same time. For the folks that say never more than one Tang it will work but they must not look anything alike. I also feed lots of greens to support all the vegetarians in my tank.
Disclaimer: I have a very unusual situation with the kind of fish and numbers. My wife does not know the meaning of NO MORE FISH so she has really over populated the tank by all conventional thinking. We have 3 wrasse, 5 gobies, 2 angles, 2 tangs, 3 anthias, 10 chromis, 5 clowns, 1 dottyback, 1 royal gramma, 7 shrimp, 1 clam, 5 anemones, blue star, orange star, 2 brittle stars, 3 urchins, 100 snails, 50 crabs, 2 flame scallops, a boat load of corals and a host of other stuff I am sure I forgot.