Vodka is meant to be colorless and flavorless, ideally pure water and ethanol.

Whiskey is made to retain flavors from the grain it isade from, and aged in charred oak barrels to impart flavors from the wood. The region of the world and the process used causes a variety of flavors.

Scotch, from Scotland, is made primarily or entirely of barley. The malted barley is toasted over a peat fire, which is where scotch gets its peaty or smoky flavor from, and that flavor often depends on where around Scotland the peat is sourced from, Islay Scotches are noted for rather aggressive flavors. Scotch is aged in used whine, sherry or bourbon barrels, so they often take on characteristics from the barrel's previous contents.

Irish whiskies are made of partially unmalted barley, which lends a unique kind of floral note.

American Bourbon is made of at least 51% corn and aged in new white oak barrels. The United States is almost all warmer than the Britain and Ireland (not a lot of whiskey is made in Alaska) so the booze interacts with the barrel differently and extracts different chemicals. Bourbons are noted for cherry, apple, vanilla and caramel flavors. Not all whiskey made in the United States fits the definition of bourbon; there's a lot of interesting things happening in the American "Single Malt" category which is Let's Try To Make Scotch, But On A Continent. Not a lot of peat bogs in the US, so hardwood charcoal is used to smoke the malted grain instead, and again America's climate means it ages differently, so the result is quite different from Scotch but still quite interesting.

Canadian Rye whiskey is often citrusy or spicy.