Attention, non-vacationing pinheads!

I gotta replace a slate roof, and am hemming and hawing about durability of
lead coated copper vs. terne-coated stainless steel flashing.  It doesn't
make much sense to me to save money by installing 25 year flashings under a
100 year roof.  On the other hand, having had bad experiences with splitting
soldered seams in TCSS, would I not be insane to insist that a roofer use
TCSS if he doesn't want to?  Are we not better off with
more-readily-solderable LCC, which theoretically should give us a longer
service life for well-soldered joints than the more durable TCSS with joints
that want to split next week?

Please advise ASAP.

Your loving humor czar,

Ralph