Best way to decide is to try the options and see which works best for you.
Some of the problems with each mode:
Low Bitrate: Poor quality image if there is a lot of movement in the image.
Low Framerate: May miss fast moving things, no audio.
Event recording: Dependant of successful detection of events, recording misses the start of the event.
Buffered recording: Dependant of successful detection of events, not available on current firmware.
So if you want to ensure catching 100% of events then it has to be low bitrate, especially as low bitrate includes audio which will record a collision even if it is not in view of the lens. The only real problem with low bitrate is that if there is a lot of movement in the image then it will loose quality, but unless you are parked on a busy highway with the trees blowing in a gale, it does seem to do quite well... at least I haven't seen many people complaining about the results...