All the "6" series remotes have identical programming abilities, so you should make your decision on which has the best button layout for you (in addition to price). The 680 is generally considered the best for PVR use, since it has the transport controls surrounding the thumbpad. Also, the chapter skip forward and back buttons are dual-labeled "Skip" and "Replay".
There are a number of threads and opinions on all of the "6" series on this forum.
There are a number of threads and opinions on all of the "6" series on this forum.