Hi Steve
I did a lot of investigation before buying mine 14 months ago. The best place to get a lot of info and comparison is dashcamtalk.com. I eventually settled on the Panorama G (now the Street Guardian SGZC12SG), because it provided all the facilities I wanted, is one of the few out there which can handle a decent-sized memory card (most are max 32gb), and I got to speak to the developer and the distributors (Jokiin, and Jon and Nico on DCT), all of whom were very helpful. One of the most important properties is HD recording. When you are at a closing velocity of >60mph, number plates are very difficult to read, and whilst there are occasions that recordings are a bit dodgy even for the 'G' (low light conditions etc), it is one of the best, especially the Mk 2 version now available. Once you decide on full HD, then a larger memory card is almost mandatory, as a 32gb card gives you less than 4 hours recording.
Not the cheapest, but you get what you pay for.
Del