it really depends what you have to pay for it
but I would suggest looking in to the bowmore Mariner(15y old), it's a tad cheaper than the 17y and if you ask me, a much better malt
The glenfarclas 15y is here (belgium) around €40, that's not too much either, the 21 is €60 ...
The Port Ellen is too expensive for what it is, not that it's not a nice malt, but then I would go for something else in that price range
and I have to concur with stig, just buy whichever one you fancy most, and have a nice drink