I think most of us are happy with them, but most owners seem real happy with any of the current heavy duty trucks - they're all really good and capable vehicles and are much more comfortable than trucks from just a few years ago.
The single biggest reason I got a Ram is I wanted the Cummins. There were some other factors in consideration of course, but if you really dig down that was the nut of it. Basically after a ton of reading and research I concluded it was likely to have the best long term reliability in terms of the engine and emissions setup. It's a simpler engine with fewer moving parts and it has a much more reliable injection pump.
From a capability and performance standpoint, you can't go wrong with any of the current big diesels.