Just some random thoughts...
The internet browser was the best I've used on a mobile device. This was on an iPod Touch, but its the same browser that's on the iPhone. The HTC is going to be a bit fatter than the iPhone due to the physical keyboard. I have not used WM 6 with Touch Flo but it looks nice.
The iPhone screen is larger (3.5") but the resolution is lower than the smaller-screen-HTC. 480x640 @ 2.8" vs 480-by-320 @ 3.5"
If you plan to listen to your tunes: The HTC doesn't have the standard 3.5mm jack. You'll need an adapter. :down
If your are into physical keyboards, Windows Mobile, and multitasking, the Fuze might be a good choice. Internet browsing via Opera is decent as well, but probably not quite as good as the iPhone. The HTC device will allow you to expand the memory with MicroSD cards, unlike the iPhone.
One thing I don't like about Apple/iPhone is everything is so controlled. Any programs, games, music, etc, that you want to install must go through Apple software. There are ways around this but it can be a pain...but you do get access to thousands of fun yet many times useless applications.
If you liked the form factor of your Tmobile Dash a Blackberry might be of interest as well.