I'm not so much fasinated with 4G and Android. I would go for the 9780 myself, BUT I am a BB person. As a Storm person and a touch screen guy, you might be better off with Android.
I think we should move this whole thread to the Android Forum and then they can better help you decide.
The G2 is an incredible device and a great HSPA+ device. The 9780 does not support HSPA+ and the 9800 is not compatible with HSPA+ either. If you want all touchscreen, then go with the MyTouch 4G.
I looked at the G2 and had it in my hands for a week... returned it and waited for the myTouch 4G... it was worth the wait and is a much better device, faster processor and more solid feel... I don't need or want a keyboard after using this for just a week... and now that I've had the device since November I'm still very happy with it.
My friend has the G2 and it's a nice device, I'm just not a big fan of the vanilla android. Mytouch feels cheap to me, but that's just my opinion. T-Mobile is going to drop the Samsung Galaxy S 4G pretty soon, which is a nice device, if you dont mind Samsung.
ok if i was on tmobile i would go for the g2. i love that its pure android and has a keyboard as well as 4g. then i would go for the nexus s, although its not 4g its an amazing phone, you have all the updates and will be ahead of any other phone theres no substitute. then i would go for the galaxy s 4g. thing looks bad a's*. then the mytouch 4g. i think it feels cheaply made. i would take these over a defy and possibly others that would be a last choice, i am a android fan but i would go get a windows phone such as the hd7 before a defy running android. then a bb