Personally I would choose the Cummins over the Powerstroke just because of Ford's engine history over the last decade. I'm not saying the new 6.7 Powerstroke is a bad engine either as a lot of people have praised it. If I could have got a better deal on a new Powerstroke than I would have seriously considered it.
I think there is a lot going on over at Ram that is good now. The available Aisin tranny is nice for the crowd that pulls some serious weight. I have the regular 68RFE in mine and couldn't be happier though I pretty much max out at 12k pulling.