I know nothing about each OEM's update plans, and that's obviously a big deal for you.
But, for the phones themselves, I have some input.
We have both a Moment and a Hero. I've developed code and tested on both extensively.
Both devices have the capability to do multi-touch with their current Android versions. However, nobody does this except us. Imagine Multi-touch (very early Beta) and PhoneMyPC (when released in the next day or two) support MT zoom on Samsung, and have on HTC devices since the G1 release 15 months ago.
We will be releasing our Multi-touch code soon so other developers can use this feature (it is a bit of psudo-MT logic that works very well, on production phones).
Beyond that, I liked the Moment's screen much better than the Hero. It was brighter. The device seemed to scroll faster and overall had a better, more quality feel to it.
However, in memory-intensive applications, I found the Moment giving Out Of Memory errors at times when the Hero would work perfectly. I am still not quite sure why that was; we simply optimized until it worked properly on all devices.
If I had to choose, I would pick the Moment for the keyboard and brighter screen. If, however, I wanted the compactness more than the keyboard and didn't mind the slightly dimmer screen, I would pick the Hero. It all depends upon what you do with your phone, and your personal choice.
Overall, they're both terrific devices.
SoftwareForMe.com
Makers of PhoneMyPC
& Imagine Multi-touch