6.0
Since 2007 will be the last year for the 6.0, I would think that you would be getting the best 6.0 .
If you wait to get a 2008, and get the new 6.4, who knows what teething problems Ford might have with that engine. When I purchased my 2006, at that time Ford was projecting the 6.4 to come out in 2007. That is one of the reasons that I purchased the 6.0 in 2006.
So bottom line is, now is a good time to purchase a 6.0
Most of the bugs have been worked out.
2012 might be a good year to buy a 6.4