sp is the basic recovery that you flash, at least I did, when you first start customizing the Droid, and since that is what I came from to the Vibrant that and Clockwork are the only two I know. Haven't used amon so I don't know how it works. I downloaded the source code for Clockwork, now all I need to do is import the proper drivers, and re-write a little bit and I should be able to flash it via adb before the night is over.
I do prefer Amon's but that's mostly because of the amount of options and that I've mostly used D/S. I can't imagine it being too difficult to port over much of the extras that AR offers to CWM, or vice versa.
It would be nice to have one recovery to rule them all. =)