HVAC ducting preferences?

[Hwy78Cruiser]

AC and heater ducting ... mine is sturdy, but old and very stiff. The stuff I see at auto parts stores looks like it won't last very long and I'd sure like to not have to take my dash apart again any time soon.

Any recommendations on nice, flexible, long lasting AC and heater ducting? Should I use the same ducting for both, or different for hot and cold? Thanks in advance!