I've driven both, and between the two, I'd take the 4runner. Here's why:
In the model years 97-00, the Toyota simply looked more streamlined than the awkward-looking pathfinder (the Nissan XTerra was the better looking of the Nissan SUVs in my opinion). The 4runner also has (in my opinion) a smoother ride. The Toyota does have a quieter engine since Nissan went with a plastic intake manifold on their engine and Toyota stayed with aluminum. Toyota also has unparelleled longevity when cared for properly. Our shop has several Toyota trucks come in for maintenance with more than 300,000 miles on them - they just seem to live forever. Also, the 4runner has a very loyal after-market following, so you will be able to get far more accessories for your 'runner than the Pathfinder.
Aside from these advantages, both are going to be similar in most other respects. Both will have close to the same power as the Toyota had a 3.4 liter v-6 and the Nissan had a 3.3 liter v-6 in those years. Both would be fairly reliable for their age and cost about the same to fix. Either way you'll get a good SUV, but the Toyota just has a few points over the Nissan...
Good luck and drive safe!