Burdar is correct: opinions will be all over the place.
Dynomax Super turbos are definitely my favorite muffler. I put them on my 70 Cuda 340 stroker with TTI's 2.5 pipes. They sound incredible and they have no droaning sound at all. In fact, a friend of mine liked them so much, he put them on his 71 Challenger 440 wih 3" exhaust.
I also have a stock 68 Cuda formula S 340 and I decided to use Magnaflows because they had the dimensions I needed for a factory look. The magnaflows sound great too but there is a droaning sound on the highway. Not too bad but you know it's there.
You won't be sorry if you go with Dynomax Super Turbos. Hope this helps.