IMO, I would not consider any tang particularly "hardy."
They have very specialized needs in terms of tank conditions, behavior, etc. They are quite prone to disease, relative to some other fish we keep. So I agree, once again, with florida joe in terms of the question...the experience and dedication of the hobbyist is probably just as important as the "hardiness" of the fish.
If you have a reef tank, in particular, remember that tangs can produce quite a lot of waste. Depending on your existing bioload, this could be an issue. They are prone to getting ick, so I recommend QT, because treating (or removing a fish) from a reef tank is no small undertaking.
I definitely would not recommend a Naso in a 125. A Kole is very much a favorite of mine, but you have to watch for mouth problems which can be common
otherwise once established they are "relatively" hardy. The "powder" tangs are often hit hard by ick.