Its a matter of preference.
I love the G1's Physical Keyboard, but the MyTouch has more memory, plus your MyTouch has the 3.5mm headphone jack.. i would kill for that, i hate using an adapter.
Personally, if i was in your situation, i would go with the MyTouch, but i am about the evolution, and as much as i love the G1, it is becoming an old piece of hardware.
Although it is you probably won't be doing any time soon, if ever, but with the extra memory in your MyTouch, Rooting opens up to more Roms that run smoother because of the internal memory, versus the virtual memory off a Memory card (BTW i only added this information for others that may be plagued with the same question)
again. go with your personal feeling on it. It is a personal decision. for personal preference.
but let us know what you decide.