HTC One looks ok, but it still kinda looks like a copy of Blackberry Z10 to me, and even that doesn`t look that good.
Personally I prefer the stilling of Xperia Z, the only thing that kinda puts me off is the talk about the screen. I don`t think anybody can say that the HTC One doesn`t have a brighter and more vibrant screen, but I think that both are good for flagship phones.
Right now I guess I`m leaning towards the Xperia Z, currently I have an HTC Sensation and it`s ok but I wasn`t that happy with it, I didn`t have any of the major problems, except for the death grip issue with wi-fi that seems to have disappeared lately... but the biggest disappointment was the update cycle, the Sensation being still stuck on ICS officially and all the custom JB roms still have lots of bugs, and looking at the level of customization of Sense 5 I don`t think that HTC One will see anything beyond JB 4.2, but it would be a nice surprise if HTC will change their tactics with updates.