After reading this thread (and many similar ones) it sounds like the OP meant to ask which is the better bang for the buck. Whether the price difference can justify getting the MKI over the MKII is not a question anyone on this board can answer for you - there is a difference between the two lenses - but it seems to be more dependent on your budget. If you can swing the MKII without putting a strain on your finances, get it, you will be thrilled. If you can more readily finance the MKI, you will still be extremely satisfied with the lens.