well the sata2's are faster with a larger cache. but as the figures show the sata1 goes at 10,000rpm compared to the sata2 that does 7,200rpm. I rekon its a pretty close call. if your building a new computer, i would put sata2 in, if your motherboard can support it that is.
Well, there wouldn't be much difference in performance if your just handling the normal work load such as text files and all that
But for big files, such as movies, then there may be a slight difference
I would go with SATA2 though, seeing as though it is better and you may not need to upgrade it as much compared to SATA1
But i would also go with price as Dishdog said