For most people I'd recommend the '98, though the differences are minor. The M112 V6 engine seems to be more reliable overall than the M104 I6. It does not suffer the headgasket and oil leak problems of the inline engine. The only weak spot on the M112 is the harmonic balancer, and this is a very inexpensive and easy repair if performed before it fails. The V6 returns slightly better fuel economy and has much lower emissions/pollution. Overall performance is about the same.

The '97 is the first year most cars got the 722.6 five speed automatic transmission. Though it's overall a good unit, there are a number of updates over the years. A '98 will likely have a few a updates that are missing in the '97.

You can get a '98 model year wagon, there is no '97 wagon.

The differences are minor enough that I'd take a clean '97 over a less-nice '98, but all other things being equal I'd choose the '98.

- JimY