Get the Duramax. I have a 09 and it is great. A Friend had a 08 Ford that had broken down many many times. The last time was pulling his travel trailer and it quit in a intersection. He had to live in the trailer on the side of the road for 4 days till the local small town shop could get to it. Then they had to order parts. His wife just traded it in on a new Duramax.
Duramax is awesome just stay away from the early years with LB7. At 160k to 200k the head gaskets have to be replaced. This is a huge job and not to be taken lightly.
Don't ask how I know.....but the best engine ever! I towed a 5000lb trailer from Auburn to Ft Bragg this summer and was passing cars on the hill climbs!