I am surprised that you don't like the Ardberg, I find it a very pleasant malt myself.
The 'basic' Lagavulin is a 16 year old, but there is a very nice 15 year old double matured Distillers Edition (as there is for Oban, Talisker, Caol Ila, Dalwhinnie, Glenkinchie and Cragganmore) which as well as being ,atured in bourbon casks is also matured in Pedro Ximenez sherry casks, which has the effect of sweetening it, softening some of the harsher alcoholic edges IMO, whilst retaining the lovely peaty, orangey, oily fish, liquorice flavours and long finish. It is at a premium to the 16 year old, but not that much.
I haven't tasted the Dalwhinnie or Glenkinchie DE finishes, but I can say that all of peaty DE malts, Lagavulin, Oban, Talisker and Caol Ila are appelaing finishes to me, whislt I have just tried the Cragganmore (which is a Speyside) DE for the first time today, and I enjoyed that enormously. Incidentally I tried the new English whisky, St Georges Chapter 4 yesterday - it was pleasant and complex, but a tad short on follow through IMO.