There's a dashcam thread somewhere on this forum.
Spend a bit of time on youtube watching the dashcam clips. Many of them show which cam was used, and the quality of each can then be assessed.
The cheap ones will be adequate for a general view, but may lack definition if number plates need to be read. They can also struggle in low sun and in the dark.
The Nextbase ones seem to be very good, around £100. Cheaper but better than adequate seem to be viofo A119 and Aukey.
I'm still trying to decide whether I want/need one, but if I do, will probably go for the Nextbase 512 which has a rear cam option.
I bought a Nextbase 212 more than 2 years ago. It was one of Halfords first dashcam offers at the time but not as cheap as the current one. I found it very good with good lowlight and bright sun performance. No problem with definition either, number plates etc were easy to see. I did a fuse box "plumb in" and the whole installation is very neat. It worked flawlessly until about 2 months ago when suddenly, without warning, it malfunctioned. Normally when you switch on the ignition, it makes a chiming noise and the screen illuminates briefly, recording starts and shortly afterwards the screen blanks with recording continuing until turning off the ignition kills the power. Now, when switched on, the chimes are heard, the screen lights off and it promptly shuts down again only to wake up with a chime, screen lights and it shuts down again and so on and so on, until you pull it off the mount thus killing it's battery access.
I asked in Halfords (it's out of warranty now) they said they'd seen this before and it's usually a defective internal battery. Went on line and googled it - a number of similar symptoms being mentioned. The battery is a polimerised widget (or something like that?) anyway, you're not going to buy it in Asda! Further investigation revealed that Nextbase quote circa £35 to replace it. So I guess it's a recognized problem?
I liked having it, especially on our journeys south into the madness that is motoring in the midlands! The picture this camera produced were very good and, I would imagine, easily up to the standard required for insurance claim verification purposes. Halfords have an offer on them right now and I'm trying to make my mind up whether to buy another - maybe they've improved them since I bought mine? Thinking of splitting the case and trying to identify the battery for a DIY replacement job! Then it could take up residency on the rear screen?
It's mounted in the Ibiza which does regenerative charging. That is to say the alternator output is ECU controlled - not dependent solely on the battery's state of charge - so, if I understand correctly, when in the cruise it charges pretty much as any other alternator does. When accelerating the field circuit current in the alternator is greatly reduced, by the ECU, so max engine power is available to do work. When on overrun or braking the ECU energizes the field strongly so that a strong charge is sent to the battery thus using some of the energy usually lost to the brakes - clever, eh? (but more electronics to fail!) I've been trying to find out what voltage this pushes the system to so that I can check it. - gonna wire my voltmeter to the battery terminals anyway so I can see what it's doing. I've heard it rumoured it can be, briefly, as high as 18 volts, which would be some amperage? but I don't actually know! Going to have a chat with the lads at AVW because it occurs to me that if it consistently pushes it that high the control circuitry in the camera may not be able to cope, which might explain this failure?
So. I won't be making another camera purchase 'till I know what the alternator is meant to be doing and then checked that it actually is!