M_I_C_H_A_E_L: I think Oldeyes was refering to the HTC Sensation. I said it makes the decision harder (at least for me) and so thats why he said not if you want to use it on XT.
I could be wrong though.
That makes more sense. I probably should have looked up a little.
The only real way to choose between the two will be to handle them both and see which one feels better to you. You may prefer Sense over TouchWiz, or the increased weight of the Sensation. All I can say is that the SGS2 is a very tough phone to beat.