Which Exchange Destination?

Hi all, After paper trading for some time, I am about to start dipping my toes into retail trading CFDs on the ASX using Invast as my broker and trading in Iress Viewpoint. When entering the Buy details you have to select the Exchange Destination, and there are quite a few choices: SOR; ASXCP; ASXSWEEP; CHIX; CHIXMID; ASX; CHIXQ; CHIXMIDQ. It defaults to SOR, but I'm finding it difficult to find a lot of information about this (to make sure SOR is the best choice for me). I'd really appreciate it if any of the more seasoned traders here could please shed some light on this and advise what they use. Thanks!