don't have any experience with Fr-Eng dictionaries on the kindle, but I will say that every French class that I've been in that's recommended a Fr-Eng dictionary recommended a Collins/Roberts dictionary. I'm not sure why specifically, though. I imagine that either would be good--they're both good dictionaries generally.

Another thing that you can do with a Kindle, which I've found helpful, is download a French dictionary so when you read a French book, you can get a French definition of a French word, which can be helpful for thinking in French and associating words you already know with new words. (rather than translating all the time)