I'm not as familiar with the N97 as I should be, but I see that its has a touch screen, a physical keyboard, as well as the Symbian OS. I'd predict it to be fairly typical, not bad, but when you're paying that kind of money for a new phone (let alone the contract fees)... Why wouldn't you get the iPhone?
I guess I'd look at it this way: The 3GS has its fair share of problems. Ask yourself if you're willing to deal with the atrocious battery life, the ability for it to get hot enough to burst into flames, the Apple-ness of it all, as well as the rather poor AT&T network. If you're willing to put up with most of that, given the fact that you otherwise have the best phone on the market right now (not just hardware, but software as well), then you should be sold on the iPhone.
If you're looking for a value competitor to the iPhone, check out the E71x. The form and function balance is spot-on, and I absolutely love the look and feel of the phone. Problem is, you still have to pay iPhone prices for the contract. And that sucks. Big time. Then it becomes a question of how much you want to invest, and how much you're paying over time.