Drinking bourbon can be a great way to find a little comfort and solace, no matter how you decide to enjoy it.
When any spirit is chilled, it fools the palate into tasting sweeter the colder it gets. Water will dilute the bourbon as ice melts, making it more fragrant. Chilling and diluting can also take some sting out of the spirit as well, creating a more balanced experience.
When it comes to whiskey ice, you can pick cubes, blocks, or spheres. No matter which you pick, they all do the same thing: melt as they chill. The difference is only the speed of dilution.
Ice cubes, especially the wet ones found in most bar wells, are not the best option. They chill quickly, but that means they also over-dilute the whiskey: bad news if you aim to enjoy one.
Blocks and spheres are both good choices for drinking chilled whiskey. They offer large thermal mass and minimal surface areas, meaning they melt slower (diluting less) to maintain a stable temperature. Because they have the least surface area, spheres have the edge… though your whiskey shouldn’t stick around long enough for it to really matter.
Whatever big ice mold you have on hand will work because they all share the same disadvantage: they’re big, which means your choice of glassware is limited to a rocks glass. This style of glass limits how many of the nuanced aromas you’ll be able to pick up… which is one of the main reasons to dilute your whiskey in the first place.
There are also whiskey stones. I’m throwing these into the mix because they allow a drinker to chill their whiskey without diluting it. They’re often expensive and are sometimes offered in metal variants. Personally, I don’t recommend any of them because of the minerals and/or reactivity from the materials they’re made of interfering with whiskey on my palate.
They’re also an expensive option to sticking a bottle into the fridge (proper temp), a tulip glass in the freezer (high thermal mass and a shape that delivers aromas to the nose) and using drops of distilled water to “tune” the whiskey’s aromas to your palate (dilution to a lower proof), leading to a thoughtful and deliberate drinking experience.