IMHO, the Passport Card is the way to go. It looks official, says "United States of America" in big letters, and I've never had it rejected (knock on wood). In fact, in recent years I haven't even gotten the surprised reaction "oh, cool, I've never seen one of these!" The Passport Card has exactly the same information as the Passport Book, making it less risky to show a TSA employee than a driver license that contains your home address.
I have a NEXUS card as well, but I have never tried it at TSA checkpoints given the frequent reports here that TSOs reject it simply because they are not familiar with it.
IME, the TSOs who ask to see your driver license typically are located at smaller airports that do not have a lot of nonstop international flights, if any. Many Midwestern airports would qualify. The TSOs at these locations probably see 80% driver licenses, maybe less than 20% passports and other IDs. When you show them something they are not accustomed to seeing, they are more likely to question it than if you show them what they are expecting to see.
On the other hand, I would be very, very surprised if a TSO at MIA/JFK/ORD/DFW/LAX reacted the way he did to the OP. TSOs at these stations see tons of different kinds of IDs every hour, including DLs, US passports, Canadian passports, LPR cards, foreign passports, etc.