New Sense. TW was pretty bad and I haven't had a chance to mess around with blur but I don't think it'd hold up to the new Sense as far as manufacturer skins go.
I prefer stock, but Sense and New Sense both look very nice. I just like how snappy AOSP ROMs tend to be and how easy they are to hack. Rocking Enomther's TheOfficial on my Nexus One, couldn't be happier.
sense hands down. ( i mean, i love the stock experience more, but if we're going with manufactor's skins, sense) motoblur looks cheap and unpolished. touchwiz....looks like an iphone with a developmental problem.
Are we limited to manufacturer UIs or can custom ROMS qualify? If so, ApeX Rom for Droid X. But if we are talking about official roms, then stock. Can't stand blur.
I got hooked on Sense with my old TouchPro and it's even better on Android. HTC has continually refined Sense and it's matured into a truly wonderful interface; I absolutely love it. I hope the new Sense HD gets ported to the EVO either by HTC or the brilliant XDA types.
Next up for me is LauncherPro (though Federico has been quiet lately)