I have most of the ones mentioned here. I don't like the M-edge one myself. I don't find it lights up the bottom of the screen on my Sony Pocket Reader and the only way to use it is with a case.
I really like the Mighty Bright Travelflex light but it can't clip directly onto the reader because of the mechanics of the clip. It needs to clip onto a case to use with the reader. I also have the Mighty Bright Xtra Flex 2 and like it but find the neck too long and wobbles sometimes.
The Xtra Flex 2 will clip directly onto the reader but it's difficult to find a good spot to clip it to the reader because the edges are too narrow. So.....it's personal opinion and every one has different likes and dislikes. What I'd suggest to you is bring the reader to the store and try the light on for size to see how you like or don't like it. I've found the stores to be pretty good in letting me try them with my reader.