Titanium

titanium is sort of nice in theory and I was a big fan of it but the only bike things that
failed on me after short road use were titanium. I had a frame crack at a weld and
then a USE alien seatpost snapped after less than a year road use from new.
I still have a 14 year old Litespeed Mtb thats fine. So I would only buy a very cheap one
as a beater. This whole "will last a lifetime" is a myth.

Titanium is immensely difficult to work and only the most highly skilled welder can join ti tubes properly. A lot of cheap ti frames and components fail because the welds are poor. It will last a lifetime if it's properly done.