I belive the 2X has 512, not 100% sure though.
As for which one to get....well, first off, I am with Sprint and I am sticking with Sprint, so it all depends on which phone they will get. Sprint has the Evo, the Epic, and the old Optimus, so something tells me that they might get top phones from the 3 big boys, without knowing what HTC brings to the table, I am not set on any of them yet, however, this time around I am leaning toward the S2 simply because of the SAMOLED+ screen. Last year I had no idea that we would get the Epic, so I was slightly disappointed in only having an Evo simply because of the Evos wussy 3d performance. This time around however, all 3 phones will have fast 3d performance, so I am looking elsewhere to help me make my final decision. I love the 4.3" screen, and I am glad that the S2 seems to have, at least so far, the complete package for me. And while I like Sense, something new is always nice. Buying another HTC device would just diminsh the new phone feel, since it will probably look and feel just like the Evo, just faster.
Time will tell.