I understand your comment that the 15yr is almost ordinary, but that may be its winning attribute. To me, the Single Barrel is what a classic "Scotch Whisky" should be, without getting into the different profiles of the regional whiskies. In other words, if someone likes Scotch whisky, they SHOULD like the Single Barrel 15yr.
When I was choosing what to put in my whisky decanter, I chose the Single Barrel 15yr.
I've never had the Macallan 10yr. I've had the 12, Cask Strength (my favorite Macallan expression), and the 18yr.
The Laphroaig 18yr is exceptional. I have a bottle of their 10yr cask strength, but went with Lagavulin 16yr for a higher end Islay.
I have tasted, but have never owned the Oban 14. I keep telling myself I'll get it next, but it is so expensive, I don't know if its worth it.
The Highland Park 12yr is fantastic. It really melds the regions into one beautifully crafted, easy to drink, masterpiece. The 18yr is good, too; but the 12 yr is the best value going. Fantastic dram. I just finished my bottle, and will have to get another. It is the whisky I drink when I'm not sure what I feel like.
The Glenlivet 12yr is so boring to me I can't even stand it. If I have already finished off a couple excellent whiskies, I would consider switching to the Glenlivet. Then again, I'd also consider switching to Cutty Sark, Famous Grouse, or one of Johnny Walkers blends at that point!
I have a bottle of the Glenmorangie Lasanta at my sister-in-law's house. I keep it there for when I visit. Its good stuff, and worth its price, but not excellent.
So, if I were to rank them (non-blinded), I would rank them as follows:
1- Laphroaig 18yr
2- Balvenie 15yr
3- Oban 14
4- Highland Park 12yr
5- Glenmorangie Lasanta
6- Glenlivet 12yr
As I have not tasted the Macallan 10yr, I cannot rank it.