Here in the UK there's no 4G (to speak of) so we can take that out of the equation unless you intend to travel to the US frequently. I think that a lot of the extra horsepower in the new iPad is there to drive the screen - which is fabulous, but then the screen on the iPad 2 is still excellent; I'd urge you to visit a local Apple store to see them side by side.
The other consideration is capacity - iPad 2s are only available (new) in 16Gb, whereas the new iPad is available up to 64Gb. And finally there's the cameras; the iPad 2 basically had a webcam and a video camera whereas the new iPad has the camera module from the iPhone 4 - very good for stills and video.
So, if you don't expect to take many photos, and you think you can live with 16Gb, then iPad 2 is a pretty good deal. If you need to take a lot of pictures, or carry around a lot of movies or photos or music, or just if you all in love with the retina display, then the iPad 3 is your best bet.
HTH Peter