Selecting whiskey for use in mixed drinks takes consideration, depending on the kind of drink you're going to make, and the kind of whiskey you maybe use. Generally speaking, I used whatever I have available, but when I'm behind the bar I have a lot more choices, and you have to be a little bit more discriminatory.
If you're going to make something that's going to be light, go with soda. The airy and bubbly, you're going to want something that's going to be a lighter whiskey, something that's going to be a little more effusent. I like blended scotches. I like bourbons. Anything that you can sip comfortably, is going to mix well with soda, ginger ale, any of those.
You can also sodas, and things like that, to mitigate harsher, sharper flavors. Dilute some of the higher group alcohols. But when you're picking a nice high-proof shot, it's usually because you want to drink it neat, straight-forward. When you're making a cocktail on the other hand, you have to consider some of the more subtle, longer flavors.
Rye whiskey, for instance, mixes fantastically in things like Old-Fashions, Manhattans. Most of your stirred cocktails will take very well to rye, whereas bourbon will be a little too round and a little too sweet once it dilutes. When you're mixing scotch, that's really kind of anybody's game. Scotch and soda is a classic. Scotch mixed drinks like the Rob Roy, the Fitzgerald, those all blend well. When you're mixing bourbon, anything goes. Bourbon is a round spirit. It's easy-going. It's something you can mix comfortably, or sip straight. What you want to think about are the after effects.
Once you start mixing your whiskeys together, you're going to eliminate the first taste that you get from the glass and you're going to get some more of the modifiers, the citrus, the spirits that you're adding to it, and then you get more of the bourbon's, or whiskey's, or rye's after taste.
So when you're selecting a whiskey for a mixed drink, think about the front and the back, and then add your mixers accordingly.
And those are some notes on how to pick a whiskey for mixing a drink.