Answer
Lactic acid's ionization reaction is more reactant-favored.
Work Step by Step
If we analyze the $K_a$ expression:
$K_a = \frac{[Products]}{[Reactants]}$
We will see that, the Ka is inversely proportional to the concentration of the reactants in equlibrium.
Therefore, the acid with the lower Ka, will be more reactant-favored.
