I’ve owned a Canon Ixus 430, Ixus 82is and the older APS version. I’ve not owned the competition so judge what you will.
However, I’ve found that the shutter lag on the Ixus can sometimes be awful, particularly indoors, when it can take a couple of seconds to lock on sometimes. It seems to go in out in out, you realise you are jamming the shutter button down and it’s just sat there not taking the photo.
I think its the multi-point auto focus, which always makes its own mind up and sometimes can’t make its mind up. Even if you disable this in manual mode, it still sometimes appears to do what it wants. Night shots usually come out blurred, typically the final shot looks a mess despite the LCD display looking fine before and after the photo. If it could just use the settings it uses on the live display all would be fine!