Ahh it's a matter of preference? Different ones incumber and can cause strain to different areas of the face I would presume? Also it gets a bit harder to say safewords so make sure you have an alternative way of signalling.
Depends on the look you want and how much you want your mouth opened up. The CCA has both ring and lips open gags. Lips are a big size so prepare you jaw to be sore after hours of wearing your first few times.