The most reliable used Volvo wagons are:

     VOLVO 240 '91 & '92
     VOLVO 940 '94 & '95
     VOLVO 850 '95 - '97
     VOLVO V40 '01 - '02
     VOLVO V70 '99-00

I would recommend either the 850 or V70 unless you can get a low mileage
240.  My personal experience is that the 850s are at least as good at
high mileages as the 240s were.

if you like the 240....try and find, and drive
one of the 1992, or so 240 wagons...we had
one and it was great, nice leather, some
options, good stero, tow package, and it was
a 240......i guess i would be looking to drive
the latest 240 wagons made...i am guessing
it was 92, 93, or 94...

V90 or 965 from the late 90s... For some reason rated as one of the least
reliable Volvo's, but I can't see how... No one seems to complain about them
on here, the Volvo dealer (maybe no one takes them to the dealer because
indy shops are cheaper... our dealer mechanics are great, so we stick with
them) we take our 960 to say they don't get in any aside from routine
service, and the odd age related component replacement (that's all our 1993
has had... pretty much any 12 year old car would have had the same parts
changed as ours... A/C seals, worn out shocks, exhaust, few lightbulbs...
steering rack leaked, could be a problem in any car, or might last longer...
every Volvo apparantly needs a new rad at around 10 years, we got 11.5 out
of ours).

I asked 3-4 Volvo mechanics: 850 or 960 - and they said the 960 is the
better designed car, especially for the expensive A/C system... They said
the 960's tend to have small leaks that are reasonable to fix (we've
experienced this), but the 850's have their components in different
locations and they tend to have failures on the big ticket items, like the
evaporator (and who DOESN'T like a car with A/C??)... Plus you are used to
the RWD (classic style) layout and stying... Another good thing, at least
around here - 960 never held their value... most owners seem to be running
them for a long time, and doing proper maintenance because of this (i've
never seen a 960/S/V90 in bad shape... even the old ones) - if you do find
one it'll be worth less then a comparable 240 or 850, at least around here.

The 240's are very good, they didn't change much from the mid 80's on. If
you want something a bit more updated feeling you could look into a 740 or
940, perhaps a turbo if you'd like a bit more zip.