I have a HTC Touch HD and had a Hero that I sold.
The chipset that HTC use appears to be the same on all their devices, which IMO is not upto the task of dealing with complex web pages etc. Works fine but very laggy compared to an Iphone.
The Hero needs some new ROM updates as the reception was much worse than the HD and the data connection kept dropping. But I am sure HTC are working on this if they havent already sorted it.
I would say that the Hero is sligtly more Iphone like than the Touch in terms of UE.
Ultimately both good phones, dont know anything about the samsung but at a guess I would say it may be faster but will probably be able to do less with it.
I stuck with the Touch as I prefered the windows OS and wasnt sure if TomTom was out for the hero.
Still I was tempted to sell them both and get an Iphone, my mate did that and it is the superior device but we all know that.