The old saying is true: Buy cheap wine and expensive liquor (and do whatever the fuck you want when it comes to beer, I guess). When looking for liquor for your mixed drinks (or for anything), stay away from that bottom shelf. Cheap liquor can ruin a cocktail, even in small amounts. If you’re buying liquor for mixing, you’ll want to spend at about $12-$20 for a fifth (750 mL). So with vodka, for example, you won’t want anything cheaper than Smirnoff, but probably nothing more expensive than Absolut (allowing, of course, for a reasonable margin of error on the high end). If you have the money, you’re obviously welcome to use a more expensive liquor, but unless you’re making a cocktail that really emphasizes the unique flavor of the base liquor (say, a Martini or a Manhattan), you don’t want to be mixing your top shelf liquor. Otherwise, you’re just wasting that Crystal Head by putting it in a Long Island Iced Tea. Stick to the middle shelf when mixing drinks.
The exception to this rule, in my experience is liqueur. Cheap liqueur tastes fine and is appropriate for mixing. Feel free to use Arrow or DeKuyper for your basic liqueur needs, figure out which liqueurs you really like, and try more expensive brands as your funds allow.