The cameras are very similar on paper, both with rich feature sets. The main difference is that the ZS100 has a larger sensor and a slightly larger wide-open aperture. Therefor the ZS100 will have better image quality and will hold up better in lower light conditions. On the other hand the ZS70 has a longer zoom, which could be an advantage depending on your needs. I just bought the ZS100 and I find the zoom is very usable at it's most extended setting in well lit conditions without needing to use a tripod. I am curious how the ZS70 performs at max zoom and it was very tempting to buy, for its long reach.