At this point I would not use up an upgrade and get the Nexus S.
The Nexus is single core and only has 512MB of ram. Ice Cream Sandwich does lag a bit on it.
If you want pure android, you could save up until you can get the Galaxy Nexus for $200.
Otherwise, the EVO 3D and the Photon are $100. I would get the Galaxy Nexus though.
But do u think. Should wait until the ics update comes for the evoke design