The main difference is the model....
The '02 9-3 you are looking at is a hatchback with the B205 engine, in SE spec 185 hp and running Trionic 7 engine management. Nice car, very thin & high-looking compared to the later 9-3's, but its a hatchback - you can fit virtually anything in it ! Handy when you have two large dogs and dont want a estate... of a couple of MTB's or lots of RC kit ! I presume you are looking at the 3-door and not the 5 door ?
Fuel economy is suprisingly good, parts are relatively cheap, its extremely quick and it dosent have too many inherent problems - the old sludging problem isnt so much of a concern these days as they will have been sorted out by now with a clean out and the latest oil breathing kit.
The '01 9-5 is the larger model, booted with 4 doors - basically larger all round. A family car. I personally dont like it myself - i still prefer the old 9000 for the larger Saab - but if you do have a large family its great. It also runs the B205 engine in 2.0 litre form, basically the same so the same rules apply as for the 9-3's engine. But larger car, slightly slower. And a bit boring tbh
Ive been a Saab fan for years for 9000's and early 900 Turbos, i had the same choice as you for a buisness car recently so i went for a '01 Saab 9-3 Viggen with the biggest engine they put in it - the B325 with 230 hp....
Great fun, cheap to run, huuuuge boot, its as quick as anything your likely to meet, and i still get 35mpg if i drive steady
Also look at the 9-3 Aero HOT up to '02 - same bodykit as the Viggen but with the 2.0 T engine. Better interiors in my opinion, and also not expensive. And a bit quicker than the SE. Oh, and if possible get a 3-door if you decide on a 9-3, they command better re-sale values than the 4 door. Early 9-5's are now cheap as chips - if it goes wrong, bin it and buy another....
If you need more info go on UKSaabs. Bets place for friendly information and advice if you require it.