For me TPO...have had both and prefer TPO. As for the KZ issue...it was in 2006 and 2007 but was also on many other brands like Jayco during that period. I had a 07 Durango that had the issue. KZ replaced the entire roof including substrate and repaired delam...all out of warranty period (2 year warranty) and at no cost to me TPO as well as EPDM were invented as commercial flat roof materials and adopted by the rv industry.