I think I'd read about the differences on a site comparing commercial applications. Obviously a different animal. The TPO required the use of heat to weld the seams I think. Or maybe that was during manufacturing. Some one will know.
It was more the relatively short amount of time it's been in service, coupled with the idea they keep redesigning it to improve the previous shortcomings, that swayed me to the EPDM.
THis topic has come up here before: http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25340316/srt/pa/pging/1/page/3.cfm
Either way I'm sure I'll get a decent amount of life from the EPDM, and the price seemed less too.