The Topkicks and F650's just don't ride the same as a Freightliner Sportchassis or a conversion. The Pete and KW's are built better cab-wise. Identical underneath.
IMHO the Sportchassis is the best value of the bunch.
One other thing that the Ford and GM can't give you- 24/7 service at intervals on every major highway in the US. If you buy it with a Cat, you triple your service points.
But in the 12k to 15k range, the Ford F-550 conversions are very attractive. More other-use friendly as well.