The best scotches I've had are as complex and intensely flavorful as a really good cognac. If you're ever in the mood to drop a few bucks on faith alone, the best liquor or any variety I've ever tasted is Mortlach 16. I have an inch left in a bottle at home that's been there a while, because I'm afraid to finish it.
The worst scotches stick to your mouth, esophagus, and stomach, and you burp campfire for like two days. To me, this includes such famous ones as Lagavulin, Talisker, Laphroig, etc. People love them, but I just can't do it. The smoke/peat browbeating you with every sip is just something I can't bring myself to enjoy.