I'd say it boils down to your need for a qwerty keyboard. If you want one, get the Z. If not, the HD is (slightly) better. I want the keyboard (couldnt imagine getting a phone without, thats why I'm still stuck with my N97) and therefore getting the Z. They are both very good phones and mostly similar. The HD has better sound (SRS; Dolby Mobile) and better camera chip and optics (8mpix vs 5mpix) than the Z. Both can do 720p video. The HD has a larger display and a slightly faster CPU. For me the HD is too big, the Z will just barely fit into the shoulder pocket of my jacket where my phone usually stays.
good point but to be honest i really dont mind a phone without keyboard but it has been too long that i owned one that had one but the sound and camera look awsome. hahahah still hard to decide tho. I will wait for the reviews before i decide but imo i will go for z.
@J.Audu: actually no, the Desire Z and Desire HD CPU's are better than 1GHz CPU of the old Desire. They are built on smaller technology (45nm vs 65nm) and they have a better GPU. Of course 1GHz MSM8255 in Desire HD will be more powerfull than 800MHz MSM7230 in Desire Z, but MSM7230 will outperform the QSD8250 in Desire.
Exactly. Here is a simple overview: http://en.wikipedia.org/wiki/Snapdragon_(processor) (DZ gets MSM723) and here is a little text regarding the Adreno 205 GPU http://smartphonebenchmarks.com/forum/index.php?/topic/61-what-is-adreno-205-and-how-does-it-compare-to-other-gpus/