We have a 95 850 wagon and 98 S70 T5M. I would say both
cars have about the same quality with the older one leading/loosing
with about $400 speant in repairs vs $140 for the 70 (both
maintained by the book and the cost not counting maintenance).

Look for a car with records and no major problems in last couple
of years. Expect to see records showing some problems in first
couple of years (which dealer should have fices under warranty).

70 series offer slightly softer ride (still pretty firm),
different interior (not better, just different). Lots of
updated parts but no major change. On the safety side, 70
series have slightly stronger B pillers, better knee bolster
protection, steering column redesigned for a bit more safety
and starting in 99 the side air bags protect the head (not
just the chest).

Ford has not had any impact on the 70 series (mine was built
in December of 97).