I personally suggest turning off dash cam microphones, though users interested in recording interactions with law enforcement may disagree. And know that when an accident happens, spontaneous remarks like 'Oh no, I didn't even see him' can damn you in litigation if there's video. Some states have two-party consent laws you'll violate if you use a cam to record the voices of casual carpoolers, Uber and Lyft customers, or friends and family in your car who aren't aware of the recording. When looking for the best dash cams, consider whether they have audio recording but, more importantly, make sure you can turn it off. This is an argument for using the smallest, least noticeable dash cam - like the Garmin Mini2. That could go badly if you were in the wrong, but don't get in the habit of destroying recorded evidence that is known or discoverable. The other person may mention it to their insurance company, and attorneys may demand a copy of what you've recorded. If you get in an accident with another driver, a visible dash camera is a sign that you have evidence. Some cams, like the Vantrue N4, let you record all three.

If you're more concerned about evidence when you're rear-ended you might want a cam that supports an additional rear window lens and records what's behind your car.

Decide which views you want. All dash cams record the 'over the hood' forward view but if you're a rideshare driver you may also want a view of the people in the cabin with you (but see my notes on audio recording below).

Bonus points for a cam that couples 4K recording with image stabilization.

Clips from a lesser 1080p HD cam might turn to mush when you do that. 4K may seem like overkill in a little device, but it allows you to better zoom in on details in a video clip and read small text like license plate numbers. I'd avoid dash cams that only use internal memory and don't allow you to insert your own card, for capacity and convenience reasons. Some dash cams come with a card, but it's usually a scrawny one so plan on buying your own. How much video a given card size will hold is determined by the specs of the camera as each will use different levels of video resolution and file compression: It's not possible to say that xx GB of storage will hold xx hours of video across all cams. Memory cards are cheap, so buy the largest one your camera can handle. The bigger the card, the longer that 'loop' of recorded video you can mine for a clip you want to save. Every feature beyond that is optional and, often, superfluous.

Then realize that all dash cams have the same core purpose that makes them unique among digital cameras: They record live (not time lapse) video as you drive, running in a continuous loop, the 'length' of which varies by the amount of storage in the cam.

Dashcam loop recording