Answer
Higher Ka value: Stronger acid.
Lower Ka value: Weaker acid.
Work Step by Step
Let's take a look at the Ka formula:
$K_a = \frac{[H^+][A^-]}{[HA]}$
The Ka value increases when the $[H^+]$ and $[A^-]$ increases and decreases when the value of $[HA]$ increases.
Strong acids have more $[H^+]$ and $[A^-]$, because the molecules ionized more than weak acids molecules; therefore, the value of $K_a$ is also higher.
