I have owned both the hm100 and hm150. Short answer, buy the HM150.
The picture quality is very similar, but the HM150 is a little cleaner. (Remember these are VERY good 720p cameras, but 1080i/p is not as good)
The controls, buttons, etc are MUCH better on the HM150. Much more professional and flexible/customizable. Plus I use a remote on the HM150 and it is great.