I was in the same position a year ago- ooohh.... iPhone 3GS, but AT&T.... ehhh. But I went ahead and got the iPhone 3GS. It was amazing... when it worked. There is no doubt that AT&T has the fastest network, but the coverage is paper-thin in my area. So now I'm back on Verizon with a Droid.
I would check to see how good AT&T service is. If it works and you spend most of the time in that area, I'd go with the new iPhone. If not, DO. NOT. SWITCH. Otherwise, you're going to end up with a iPod touch that costs $70/month for starbucks wi-fi. At work I would miss 7 calls from my boss and he'd ask me if I had my phone turned off. I'd miss going out with friends because my apartment has no coverage and miss their calls and texts, it was totally unreliable. The reason why I changed back to Verizon is because I got fired and had to find a new job. I just did not trust AT&T. I did not want to talk to a potential employer and have explain why this is the 5th time the call dropped, or have the potential to miss a call.
I love the iPhone, and the iPhone 4 looks fantastic. But I'm so much happier with my droid because it works. I can make a call. As far as I'm concerned, the iPhone platform is dying because of one thing- AT&T. And my advice to you is not to wait for a Verizon iPhone.
I don't like the Incredible's screen. Not a big fan. I think my Droid screen looks better.