If you own a DSLR already then you probably want a good balance between cost, portability and quality. Sensor size tends to dictate the upper ends of quality which requires some of the more expensive portables. They tend to only make it to the top end of portables your Canon G Series.
Optical zoom is def an important spec, but also watch the F-stop factor. Available ISO or sensitivity to light is the other one. Again these are better handled by larger sensors and more recent cameras.
Things like battery life or size (do you want replaceable AA's for emergency situations) could be a factor but are less likely if you are used to carrying a DSLR. Weight too if you want to pack light or not wanting to lug something around all day.
Peronally I've been eyeing up the Canon S90,S95 and now S100 (lol been looking for a few years now). To me they strike a good balance between features quality and portability.