The only thing bigger than an EVO is the Dell Streak (5" screen vs. 4.3"). Not sure what the screen size is on the HD2, but it can't be bigger. It could have a higher resolution, but I don't know the specs on the HD2. If I was going to pick a phone from the lineup today it would be between the EVO and the Nexus S. The Nexus S is missing some key features that a lot of people are barking about, but it's only day 2 of the release and there is already an update rolling out for it. That says a lot about this Sprint/Google partnership and their commitment to keeping this phone up to date. However, if you get into rooting and roming, then there really isn't a large difference between the two phones. Nexus S has a Humming bird 1GHz Proc and the EVO has a 1GHz Snapdragon Proc. The Hummingbird proc has a slightly better graphics chip. The Nexus S also has a better screen, super AMOLED which uses less power and could add to better overall battery life.
The EVO 3D will be out some time this Summer. That's as much as we know. Guess you could try out a few different phones using the 30 day clause to bide your time for the EVO 3D?!?
Update: Looks like HD2 is the same screen, size and resolution...
HTC - Products - HTC HD2 - Specification