Let the hive mind of Engadget get that for you.
"I just switched to Sprint from Verizon about three months ago for the Pre. Then I went for the Hero about a week ago. Now, I miss my hardware keyboard and am thinking about switching to the Moment. I am still able to switch back to Verizon if I want and get the Droid when it arrives. Should I just trade up to the Moment when it comes out, see if I like it, and if not switch to the Droid? Or something else entirely? Help!"
What are you talking about not too big not too small? If you consider screen size the Diamond is unnecessarily huge. They are overall close to the same size but the screen sizes(not resolution) aren't even close. Bad design by HTC IMHO. If I'm choosing a device based on media use it's not even close. The iPhone wins by a mile.
Once you get used to a nice size screen, going to a smaller one is like downgrading your phone -- especially if it is a touchscreen.