what exhaust brakes you guys prefer & why?

All I can say is I'm very happy with the factory system on my '13 Ram.

My father and I both have the PacBrake on our 2004 and well satisfied. Both installed within a month of purchase. Only issue with either is I had a pressure switch go bad.

I have the Mopar branded Jacobs exhaust brake that I had installed about 1 year after buying my truck. It works great but if I had to do it again I would buy the kit direct from Cummins. Same parts, just a lot cheaper through Cummins than a Dodge dealer.