The set of numbers that is always rational is integers.
Rational numbers are defined as numbers that can be expressed in the form of a fraction \( \frac{a}{b} \), where \( a \) and \( b \) are integers, and \( b \neq 0 \). Since integers can be expressed as themselves divided by 1 (e.g., \( 5 = \frac{5}{1} \), \(-3 = \frac{-3}{1}\)), all integers are rational numbers.
While decimals can be rational (like 0.5), they can also be irrational (like 0.333...). Positive and negative numbers can also include irrational numbers, so they are not always rational.
Thus, the correct answer is integers.