HTC build quality is one of the best, their UI is great. Sony's UI is pants and their phones aren't the best design, my sister in laws x10 mini is so thick,they should have called it the SAF (short and fat). Samsung have a decent UI, quite like stock Android/ADW Launcher, I've heard lots of people moaning about their build too.
They're having to cut back on the Desire because the Desire has a 512Mb capacity rom. If it gets the new Sense, it'll be worth any cut backs imo. Root the X10 and get rid of the fugly UI by installing a different rom.
the x10 mini is a joke and cant be compared to an x10, its like comparing the wildfire to the sense, half the phone, the x10i is a very well built and good looking phone, there ui in this one isnt as bad as old ones but the mediascape and timescape crap does piss me off, besides this i really do think that if theyd updated it when it was released instead of keeping it on 1.6 then it would have sold a lot better and scored higher in people estimation.
ive already rooted the x10, i would have a different rom on but the camera sucks on all them, vga at best and lose video completely, once the newest update is out i will defintely be upgrading
i used a workmates galaxy for a short while and got wound up quite quickly, i seem to get this on all samsung phones, he managed to snap his phone in half when he sat on it so build quality definately an issue, but there way ahead when it comes to development of android, theve released a free sg2 to developers to see what they can do with it, quite cool i reckon