Normally, when comparing Acid Strengths between two acids, the first criterion used is their respective value for Ka at the same temperature. Obviously the one with a higher Ka at the same temperature is "stronger".
If you have two different acids (let's say HF and HCl) with the same pH, their strength can be compared in terms of their conversion ratio (a ratio that represents acid dissociation in solution).
Conversion = ax/CAo
a = stoichiometry coefficient for the acid in its dissociation reaction;
x = change in acid concentration to reach equilibrium;
CAo = Initial concentration of acid
For both HCl and HF, a = 1 due to their corresponding dissociation reactions.
For HCl, it can be assumed that CAo = x, so its Conversion is 1 or 100%
For HF, CAo >> x, so its Conversion is << 1 or << 100%
Therefore, HCl is the stronger acid.
However, since you're comparing the same acid (HCl) at different concentrations (and same Temperature, I'm assuming), concentration should be used as a secondary criterion because both the Conversion and Ka remain constant.
Since 3M is higher than 1M, the former should be regarded as the stronger acid.