guess i'll chime in with my 2cents.
i have the mytouch3G (MT3G), or dubbed as HTC Magic in asia. i've updated to the 1.6 donut and noticed there's still a lot of room for improvement. the phone itself is fine, great for multi-task, but starts to slow down once you load a lot of stuff in. i've even kept most of the icon away from the home page. compared to my 3Gs, 3Gs wins hands down even with 3 pages filled with icons.
notification bar is wonderful on the MT3G, which is something I wish I could have in the 3Gs. the touchscreen on the MT3G is fair, the edges of the screen needs a lot of pressure and not always picks up on the dime like the 3Gs. 3Gs is glass sensitive, and the MT3G is more like pressure sensitive type.
the MT3G or droid like type of phone will get ppl hooked if you are addicted to Google apps. for me i travel a lot, so i depend on google apps quite a bit. so needless to say, with the MT3G, i can use a lot of google app directly without having to open up a new browser for it, like the 3Gs. most of all, i can direct dial out or SMS out using my GV, which 3Gs doesn't.
as for battery life, MT3G on a fully charge battery, with LCD brightness turned down, i can use it from 7:30AM till 11PM at night (without wifi, GPS turned on) before i need a recharge. With the 3Gs, it's about the same, but a couple hrs better, even with the wifi turned on.
so both has pros and cons. with Tmo, 3G network is slow on the MT3G. but i know that depends on the area where i live. EDGE is faster for me on the MT3G and much better on battery life. with Tmo on 3GS, i can only run edge, but with the power processor on the 3Gs, EDGE is faster than MT3G.
so that's that. i love both, cuz it all has it's pros and cons. the best would be to have a 3Gs with direct Google features, cuz i hate the fact that when i run a google app in 3Gs, it opens a browser. super annoying. next thing i know, i have like 8 browsers opened. oh well...
oh, i forgot to mention.. google's free GPS navigation app coming soon to droid base phones with turn by turn and it's FREE@!!!!! can't wait for that. if someone knows of a free turn by turn for 3Gs.. let me know!!