There are a lot of brands, but most use the same internals, in fact the last few reviews I've seen it looks like there are only really 3 companies making the chips, everyone else just adds their housing and flair. I have one by Viofo that uses capacitors instead of a battery backup. This means that I don't have the continuous monitoring, but in my old car that doesn't matter, and the temps my car sees during the day is a battery killer. Viofo is one of the OEMs, not the best, but they are often the cheapest for a given capability. Mine has a screen that is mostly just for focusing it, although you can do playback on it. and the night performance is decent when the window is clean, keep in mind that at night they all flair some. Watch a few review videos that have several side by side comparisons and you will see what I mean.
As for memory cards, buy the good ones, like the mentioned samsung endurance, but get two or three and rotate them every couple months and check that they are recording, and since they are cheap, you are better off with a few smaller ones and replace them annually like your smoke detector batteries (if you still have the 9v ones) than spending a lot on just one big one that will fail at the same rate as the smaller units.
As for install, there are a few ways to do it, but if you want it to look nice, most car audio places will do it for a fee, even if you bring in the one you bought yourself (although I'm sure they would prefer to sell it to you), or you can run the wire yourself, In my case I just have it running to one of the two lighter ports in my dash because my rig is pretty rural looking.
Another factor that is worth thinking about. If it has a GPS, it will embed your speed into the video file, that can be helpful if you are in places that are hard to identify or you might need to get a location later. But also, know your local laws, as you might not want to use that video if the GPS thinks you are going a little fast. In my experience, the GPS tends to show your speed as a little slower than the speedo, but only by 1-5% or so. That choice is yours, but they almost all can have that feature turned off, so not the biggest deal, but if you know your driving habits you will know if you want that feature on or off. Same with the microphone, if being on the phone in your area is legal or not, might be something to turn off.
That said, a lot of times a cheap one will do a decent job of at least showing what was going on before the accident, so while you might not always get a plate number from a hit and run, you can at least prove that's what happened, and thus save yourself the headache of someone questioning your side of the story.
