In the early days it was guess on what did and did not work to make the 6.0 solid. Now its well known what you do and do not need to do. Some will say they are junk, but I bought a 2006 2 years ago, made the proper repairs and she tows a 14k 5th wheel without issue.
What you will find is the brand loyal that got fedup with the brand, and the brand haters will tell you buy something else. I think its a solid motor once you UN ford engineer it. As for the GM and Cummins, both great motors as well and both have their own versions of issues. Though the ISB 5.9 was a rock its also old and long in the tooth chassis make them less desirable, the ISB 6.7 has had some very annoying issues if you ask fleet owners that rack up the milage on them. The duramax has its own set of quirks and issues.
Oh and I used the 6.0 rep to chew the price down to a steal then. When most with 100-120k miles where going for 22-23k, I bought mine at 16k. CC SRW long bed Lariet with all the bells and wistles.