See explanation below.
Work Step by Step
We know that pKa of formic acid is 3.74 and pKa of acetic acid is 4.74. Formic acid would be the buffer choice as its pKa is closer to the desired pH. If acetic acid is used, the buffer component ratio would be far away from the ratio of 1:1.The NaOH serves to partially neutralize the acid and produce its conjugate base