I'm glad you have backpeddled from your clear anger over Google/HTC from your last post.
Your question about why to buy an N1 now is kind of odd given you are well aware the stats are better than the Droid and identical to the Incredible/Desire. The simple answer is the same it has been since Google decided to release a phone. Google will always release updates for the N1 before any other Android device even sniffs a new version, and in many cases we are talking 3-6 months or longer to get said update.
As for the Evo or the iPhone, the same rules apply as they always have when selecting a phone. You are comparing apples to oranges there. At this point, it's either you want an iPhone, N1/Desire/Incredible, or an Evo (between the choices you listed). The three camps are separate enough in features, size, etc that making a decision is just as personal as picking which TV you like. The tech is all cutting edge, so it comes down to what you like.