cummins hands down. the 6.9 was a good engine but a bit down on power from the cummins. the 6.2 doesn't even compare to either of these. in the pre-psd era, the turbo'd, intercooled I-6 cummins had the advantage in power over the non-turbo V8 6.9. as far as reliability goes, they are about the same.

disclaimer: i do NOT like the cummins more than the psd. but this does not concern the psd.