Given the 6.0 person said he was tired of it, I would pass. I personally loved how my 6.0 drove after I tuned it. My engine was fine, but everything else broke on it in the 30k I owned it. A proper running 6.0 is a fun pickup to drive. And the torqshift in those years is a great tranny.
However, I think the biggest factor is the debate is how much they improved the actual pickup itself from 06 to 08 with all 3 manufacturers. My 06 Ford sagged a ton when hooked up. Where my 08 Duramax still barely squats (tho I need new shocks). That being said, I have read a lot about how people don't like the Dodge tranny in those years. Although if you don't put to much power to it in a tune, I guess it's fine.
Good luck with your choice.