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What I am currently using is kind of unimportant because no matter what you choose it is outdated in about a month. What is important is field of view.
I currently have two dash cams, both with about a 180 degree field of view, and one biased to the left and the other to the right. I can pick up a car passing on the left just before its nose begins to pass the bus. Ditto for the right.
If I wanted to have the ideal set up I would also have cameras to look down both sides and across the rear. My main concern has always been to record other drivers that see a bus owner as a source of revenue, and intentionally pull in front and slam on the brakes to cause a rear end collision. I have that ability, but you may want more coverage.