Expounding on sammy's comment, when you divide $F_D$ by $F_N$, since $F_D$ only is measured to one significant figure you can only report $\mu_S$ to one significant figure.
Value of $\mu_S$ from calculating the mean of all experiments: 0.262 = 0.3
Value of $\mu_S$ from linear regression: 0.311 = 0.3
So for your case you do get the same answer either way.
If you would take a ton more data points with more significant figures on $F_D$ you should still get the same answer both ways. It would probably be a crapshoot to guess which way will give you a more accurate answer with four data points. Plotting the data points and looking at the regression will at least give you a heads up if the experiment shows non-linearity (which would be an indication of some limitation of the experimental setup to reflect the model).