Best single-malt Scotch...

I like the Islay scotches as well (I am very slowly nursing a bottle of 30yr Laphroig).

But, I like other scotches too. A friend, who is into cask strenth stuff has a nearly 30 yr old bottle of Brora that is fantastic. I usually find drinking scotch at cask strength to be a bit too harsh an experience, but this bottle was a notable exception --smooth, well balanced, with just enough peat to please someone who likes peaty scotch (doesn't have the iodine taste that I like in Islay). This friend also has some odd-ball stuff like "Scotch" distilled in Japan that had a very peculiar nose but was quite pleasing (can't recall the name). Tomorrow, he is hosting a poker game, so I am sure I will get a chance to sample yet another bottle or two.

I love the Laphroig 30yr! Truly a sublime malt,maybe the best ever. I have a couple of cask strengths including Laphroig 10 and a Bowmore 15. It can be interesting to experiment with because you should add water to it and the amount is the experimental part.I have found the Laphroig to need quite a bit to truly bloom.There is also a Laphroig small cask but I have not had the chance to try it yet.

Heading off to Ireland in two weeks and was wondering what single-malt Irish whisky I might look for.

There are few to no single malt Irish malts. Irish whiskey is a blended whiskey. I know that there have been such things but they are not mass produced.
Irish Whiskeys are different than Scotch. Usually lighter with much less smoke but with some peet. Much more palatable to the neophyte,but less desirable to the seasoned single malt taste.
of course IMHO applies.

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That's what I figuring, Emorrisiv. My go-to Scotch are Lagavullin and Talisker.