I would not recommend either of those for a car that you don't want to put some money into.
The early (pre 2003-ish?) S80s seem to have a lot of problems, and the T6 esp.
The 2001 cars all had transmission problems from software problems and poor fluid maintenance practices (Volvo recommended zero maintenance, and that is generally what is done).
Either of these cars /could/ be great, and not have any of the common problems, but I wouldn't bet money on it.
If you're looking for low maintenance costs, it's pretty tough to beat a 1998 NA (non-turbo) S/V70. Manual vs Auto is a toss up - the clutch master and slave cylinders wear out on the manuals (around 150k-200k and it's an expensive repair requiring the trans to be split from the engine), and the autos often have their fluid neglected and suffer more damage than necessary, esp in mountainous regions and on towing cars.
The turbos aren't much harder to take care of, though they do need a bit more discipline with oil changes (can you count on prev owners for this?). Volvo's turbos seem to be pretty durable in general, and the 850+ seems to be tougher than the ones used on -700s IMHO.
After that I'd pick a 2003-2007 V70, or a 1996-1997 850
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1998 V70 AWD->FWD Turbo 200k+
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