To call it "Scotch whisky" it needs to have been made in Scotland or offshore islands; see map of Whiskey producing regions in Scotland
. "Scottish Whisky" or "whiskey" is whisky made outside Scotland, perhaps in a Scottish style (but not entitled to be called "Scotch").
In terms of sales: I think you'd have to subscribe to an Industry Body newsletter to get firm numbers.
The top sellers are the blended varieties, like Teachers (cheap end of market), Dewars, Johnnie Walker, Cutty Sark, The Famous Grouse.
In terms of drinker opinion, single malts come most highly rated.
My grandmother swears by GlenFiddich
-- the world's best selling single malt Scotch, which is probably a way of saying the favourite among Americans. Still, I guess you could say that has the most votes going for it..Glenmorangie
is actually the best selling single malt whiskey within Scotland itself.
Talisker, Cadenhead Cask Strength Sept 95 bottling: Got 10 out of 10 on this web page
The other Scotch whiskeys that tend to get top marks are (alphabetical order):
Ardbeg 17 year old
Glenfarclas 25 year old
Highland Park 12 year old pure malt
Lagavulin 16 year old
Laphroaig 10 year old
Macallan 25 or 30 year old
Springbank 12 or 21 year old
Talisker 10 year old