Why not the SD card? Cheaper, smaller and easy to
interface! :)
My gut feeling is that compact flash will live a little longer in
terms of being able to get interface hardware a decade into the future.
But I could be wrong and SD might have more legs (certainly fewer
contacts). And as you point out the serial interface to a SD card is
very straightforward so I think you have a good point!
As far as I know, both CF and SD cards are docuemtned. The only custom
interfce hardware is the connectors ;-). Although it might be slow, there's
nothign to stop you talkign to an SD card by bit-banging the signals on
the I/O pins of any microcotroller, computer, or whatever.
So I see no reason why you won't be able to read/write SD cards in 10
years time.
-tony