Since I have not had any experience with any of the other Android phones my experience is limited. I have not exactly used an iPhone either. I really hate Apples business practices..
I chose the Dream because well, I didn't have many options from Rogers, and I really wanted a qwerty keyboard. I despise touch keyboards. However I can install a touch keyboard if I choose. I'll prolly be suckered into one when I root the phone and put the
Cynanogen Mod on it.
What do I like about it? It is built on Linux. Fairely intuitive interface, and I'm pretty free to do whatever the heck I want on it. The Dream has a really handy trackball that actually works. The only thing I don't like is that the battery life sucks. But that is well documented and there is plenty of free apps to reduce battery. For myself I turn off the 3G, wifi, bluetooth all the time unless needed. So SMS and phone calls still work. I get about 3 days of battery life using it lighty. Its be come my mp3 player of choice, once I installed Meridian music player on it.
Derr... still playing. Its not a powerhouse for sure. Rogers Dream comes with Android 1.5 installed. So kinda dated. But well supported. The XDA Dev's always port all the new stuff back to the G1/Dream.
I don't know anyone else with an Android phone. Everyone is Apple Fanboys. Or buggy WinMo phones.
Oh to get the most out of it ya gonna need to setup a Google account.