I'm getting one because I was unhappy with the g1... I had it for only a week, then I returned it. It was too big, to clunky, battery life was wack, the keyboard was average at best, and overall, the build quality was poor IMO. The myTouch is slim, sleek, has more ROM for apps, feels sturdy in the hand, and has improved battery life.
I looked into getting a Hero, but see no point in paying well over $500 for a phone, when it wont even have T-Mo USA 3G. I don't need a hardware keyboard, nor do I want a smaller screen, that rules out the Moto Morrison. And IF (big if imo) the Samsung Galaxy comes to t-mo usa, it wont be for at least three months, and I don't see a point in waiting 3 or more months just for a 3.5mm headphone jack... I had a pearl that has the jack, and never used it once: I carry an ipod with me at all times.