Outback is longer so you get a bit more interior space. Similar ground clearance. 96-99 will have the DOHC EJ25 which is prone to headgaskets blowing.
Forester is shorter. 98 has the DOHC EJ25, basically same as the Outback. 99-02 get the SOHC EJ25 which is prone to headgasket seepage. Not a...