Hey Reefjunkie, having a nice collection of tangs is always a sight in reef tanks.
Tomini - agreed, one if the best tangs out there as far as cost, looks, and demeanor.
The powder brown and white cheek I'd stay away from if you're looking for hardy. They are very similar to requirements needed for a powder blue tang.
Sailfin is hardy as you can get but they'll get really big. Good for a long time in a 6' tank but waaaayyyy in the future, you may need to upgrade or rehome. We're looking at at least 4-5 years before that is needed depending on the size you start with. Great fish but slightly territorial so you'll probably want to add as a smaller specimen or the largest but last.
I've never had a kole tang and yellows are so common I tend to stay away from them. Plus, the craziest tang I ever had was a yellow so I didn't feel the need to stock another one.
Some other hardy ones to look into are orange shoulder tang (cough cough, I have a large 6" one I'm rehoming), hippo tang (cough cough I have a yellow belly one I'll be rehoming), chocolate tang, lieutenant tang, tenneti tang, naso, and chevron.