That says it all, Willie. As you know there is a Spey fishing rennaissance of sorts going on in the pacific northwest's steelhead mecca - but even this legacy's namesake comes from the very waters you suggest.
I've been thinking about this one for some time and it depends on your definition of "best destination".
If the measure is pure catch statistics then three places come to mind:
1) The Junction pool on the Tweed at Kelso (Scotland) particularly the last two weeks in October, but used to tough and expensive to get a rod early and late season as well.
2) The Grimersta system on the Isle of Lewis (Double figure catches often made during one day).
3) The Ridge pool in the R. Moy (Co Mayo, Eire) in late May early June - double figure catches (mostly grilse with the occaisional salmon up to 13lb) used to be common during low water periods - they introduced a bag limit a few years ago!
But there are other definitions of "best destination" and I would agree with WillieGunn that for sheer beauty and luxurious accomodations the Tulcan beats on the Spey take some beating. I was lucky enough to fish there in the autumn of 1991 (not the best time of year for Spey) but it was simply magnificent.