My advice is to use google (groups).  I'm pretty sure this one has been
covered eleventy billion times before.

Model info -

A'98 is the last year of the (new generation) 900, popularly known as
the NG900. The NG900 was introduced in '94 and most of the bugs had
been well worked out by 1998. In 1999, Saab introduced the 9~3, which
was really just a revision of the NG900 (to the point that about 90%
of the parts still exchanged directly).

Either model is well refined. I don't know of any "big changes to the
model" differences that would cause me to stay clear of the '99. The
one major difference in 1999 was that they went back to a hydraulic
clutch instead of a mechanical clutch as in the NG900. The manual
clutch gets a bad rap but the only real issue is that the $50usd ($125
installed) cable wears out every 50K miles. Otherwise, the mechanics
of the cars are so similar as to lack distinction. If you are looking
at a convertible, I believe the top went hydraulic also in 1999 but I
may be off - it might have been 2000 for that.

Each year was a fairly well worked out model with all of the TSB's
from the preceding years incorporated. I would not have any year
specific concerns about either. If you would like, I can list a few
"things to look for" for either model. It would help if I had some
idea of the number of miles (range) you are looking at.

Mileage will depend on which motor you get and how much you like to
feel the turbo push, but all of these models tend to get 22-25 city,
27-32 highway. There were some non-turbo models which do about the
same. Most of us average around 25-27 mpg depending on our driving
mix, ambient temperatures, and style.

Parts are as reasonable as any car these days. Labor is more in the US
than more common cars - mostly because th dealers charge more so the
indy's think it's OK to stay just a few bucks below dealer prices.

Resales tends to be lower for Saabs - or looking at it another way -
they tend to lose value after the initial dealer sale. The reason is
that any car of a particular quality and refinement costs a certain
amount to produce. So, Saabs sell for prices similar to any other
comparable car when new. However, Saabs tend to be a bit "cultish" in
the used market- so there's less demand, That means they seel for
lower prices used - which is good for a smart guy like you who is
buying used. After the initial depreciation off the lot and through
the first couple years, they depreciate fairly normally.

Bob

Goodo!  Other people have detailed the background.

This can be expensive.

In UK terms, the petrol models are all pretty similar for consumption.
Their official book figures are typically ~19 for the urban cycle and ~40
for the extra urban cycle with combined cycle figures of around 30 to the
gallon.  The diesel, well, you're looking at ~32, ~61, ~46 respectively.

The sweet spot of the range is either the 2.0t (150 / 154 bhp, 2.0, low
pressure turbo) or the 2.2 TiD (but I like diesels so I'm biased).  SE
specification gets lots of toys but optional heated leather interior.

I particularily like the 2.0t because it produces decent thump lower down in
the rev range, Saab have given it reasonably tall gearing so it's quiet on
the motorway but picks up nicely when you give it a boot.  It doesn't need
revs for decent acceleration (unlike the non-turbo 2.0), which probably
helps keep consumption down in real world terms.  The 2.2 diesel isn't all
that quiet at idle but on the move it has a lovely* diesel thrum about it,
its multivalve 2.2 engine is keen to rev beyond the red line and it's also
not too bad on fuel.  It is no economy champion but mine returns ~50 mpg
with my driving.  That's why I run the diesel, I'm tight.

I'd avoid the 2.0 non-turbo.  It's just as thirsty as the other machines, it
feels slower than the diesel on the road (despite being more powerful) and
whilst it doesn't have quite the same traction issues as the turbos, it's
just, well, erm... not as nice as the 2.0t.

The 2.0T has 185 or 205 bhp, feels perky in the upper gears.  The 2.3
non-turbo is smooth but not especially rapid, it has ~150 bhp as I remember.
The 2.3 Viggen is viciously quick... it feels silly.  230 bhp or so, front
wheel drive, what feels like short gearing...  Lovely.  And no thirstier
than the boggo non-turbo 2.0 either. :-)

...but all 9-3s of this generation are limited by their traction.  They
wheelspin.  Lots.  Even the 115 bhp diesel without it being chipped.  It's a
Saab thing...

Of this age, they're cheap.  They will get cheaper.

First off, find out if there's a decent Saab specialist nearby.  I live in
York, I use a specialist in Boroughbridge, Griffin Autotechniks; they're
materially cheaper than a Saab main dealer but they know their stuff.

Secondly, get yourself down to the Saab forums and read up on the common 9-3
issues, such as the SID screens not working, the diesel's duff mass air
meter and importantly the bulkhead seperation issue type thing.  These are
not to put you off but to help you spot it...  I bought my 2000 TiD with a
duff mass air meter.  It's a £250 part from Saab, I knocked off £400 from
the price and found a nearly new but used spare for £60... :)

Things to note about the 9-3 include the fact that the interior should be
rattle free, the heater and air conditioning should be powerful, the car,
well, solid to drive if uninspiring in the ordinary models.  Don't get me
wrong, I like the way my 9-3 TiD drives, but it isn't exactly sporty
feeling.